Conservation of Underwater Archaeological Finds Manual 2-Libre

8/12/2019 Conservation of Underwater Archaeological Finds Manual 2-Libre

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International Centre for Underwater Archaeology in Zadar

CONSERVATION OF UNDERWATER

ARCHAEOLOGICAL FINDS

MANUAL

II. edition

Zadar, 2014.


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CONSERVATION OF UNDERWATER ARCHAEOLOGICAL FINDS

MANUAL

This Manual is intended for use at Advanced Course on the Restoration and Conservation of UnderwaterArchaeological Finds

II. edition, Zadar, 2014.

Editor: Beki5Luka

Authors: Beki5Luka4urkovi5MartinaJeli5Anita

Jozi5AntonijaMartinovi5IvoMusta7ek MladenPerin TanjaPei5Mladen

Expert advisor: Tran Quoc Kho, Atelier Rgional de Conservation ARC-Nuclart CEA-Grenoble, France

Translation to English: Feren7i5Neven

Graphic design: imi7i5Marina

Press: Futuro I. S., Zadar

Edition: 200

Publisher: International Centre for Underwater Archaeology in Zadar

B.Petranovi5a 1, HR-2300 Zadar, Croatia

CIP-Katalogizacija u publikacijiZnanstvena knjinica Zadar

UDK 902.034(497.5)(035)

CONSERVATION of underwater archaeological finds : manual / . - 2nd ed. - Zadar : International Centre for Underwater Archaeol ogy in Zadar, 2014. - 116 str.: ilustr. (preteno u bojama) ; 31 cmBibliografija.

ISBN 978-953-56855-1-7

1. Beki5, Luka140801029

Not for sale

This Manual was initially created with the support of the UNESCO Venice Office.

I. Underwater Cultural Heritage and the UNESCO ConventionBeki5Luka

7

II. Guidelines, Ethics and the Methodology of Conservation - Restoration WorkMusta7ek Mladen 14

III. Causes of the Decay of Archaeological MaterialMusta7ek Mladen

17

IV. The Conservation and Restoration of Ceramics and Pottery4urkovi5Martina

26

V. The Conservation and Restoration of Glass4urkovi5Martina

39

VI. The Conservation and Restoration of Metal FindsJozi5Antonija

47

VII. Organic MaterialJeli5Anita

60

VIII. The Conservation and Restoration of Stone Finds

Martinovi5Ivo76

IX. The Handling, Packing, Transport and Storage of UnderwaterArchaeological FindsPerin Tanja, Jeli5Anita

84

X. In situ Protection of Underwater Cultural HeritagePei5Mladen

97

BIBLIOGRAPHY 108

INTERNET SOURCES 113

CONTENTS


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Beki5L.: Underwater Cultural Heritage and the UNESCO Convention 7

I. Underwater Cultural Heritage and the UNESCOConvention

INTRODUCTION

Sunken ships, settlements and various otherhidden and valuable finds in the depths of thesea have always stirred the interest of peopleand their desire to reach them. The motivationsto access these sunken traces of human pre-sence have been diverse. On the one hand the-re is the ever - present factor of human curiosity,desire for knowledge and an understanding ofevents around us and over time and, on the ot-her, a desire to gain wealth, including valuableand rare material property.

The traces of human activity that have disappe-ared under the waves were once sundered fromour onshore existence by the significant obstac-le of underwater depth. With time and humanprogress this obstacle has largely been overco-

me. Sunken human formations (features) beca-me increasingly accessible. And so people, irre-spective of the desires that motivated them, fo-und it easier to access the environment of thesesunken formations and act upon them. A great

deal of this human activity has led to theexcavation, relocation, damaging and removal ofmany underwater finds, whereby the sunkenformations have lost their characteristic attribu-tes and disappeared - a fact that has evokedconcern.

Particularly detrimental were the many activities

in which sunken objects were collected solely fortheir commercial value - a concept that gave noconsideration whatsoever to the essence of thefind site and its future.There are many examplesof various unscrupulous enterprises (treasurehunters) that, under sundry arrangements,extracted (salvaged) numerous valuable finds, inthe process destroying all the traces and datathat might have been collected.

Luka Beki5

[email protected]

Figure 1. Typical representation of a myth ofunderwater treasures (www.etsy.com)

Figure 2. Geldermalsen shipwrek auction catalogue(www.china.org.cn)


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Conservation of Underwater Archaeological Finds - MANUAL 8

The wreck of the Tek Sing was looted in the So-uth China Sea - over 300 thousand pieces ofvaluable Chinese porcelain were salvaged in1999 and later sold at auction. A British operatorsalvaged over 126 gold bars and 160 thousandporcelain items from the wreck of the Dutch ves-sel Geldermalsennear Nanjing, later sold at au-ction. Certainly the richest shipwreck is the Spa-

nish galleon Nuestra Seora de Atocha foundoff the Florida coast and ransacked by a privatecompany in a most destructive fashion to extractits cargo of gold and other objects, subsequentlysold through various channels. The list of lootedshipwrecks is a long one and still growing.

As a result, the period following World War IIwas noteworthy insofar as consideration wasgiven for the first time to the need to afford morecare to the methods of accessing individualunderwater finds, with the aim of properly pro-tecting and researching underwater human heri-tage and preserving as much of the remains aspossible for posterity. As a counter to the lootingundertaken by various private enterprises thepast half-century has seen a broadening of the

scientific approach to the research ofunderwater heritage, which encourages a res-ponsible attitude towards underwater culturalheritage. These research endeavours, crownedby comprehensive publication of the results ofresearch and the exhibition of finds to the widerpublic have raised the level of awareness of thereal value of this heritage.

Estimates put the number of sunken vessels inthe world's seas at over three million. A greatnumber of once populated settlements are alsonow underwater, as are many other diverse andnot easily discernable traces of habitation andactivity. That truly valuable cultural heritage is tobe found underwater is more than evident.

The past few decades have seen numerous initi-atives at the national level, and a great manylaws and regulations have been adopted gover-ning the methods whereby underwater heritageis protected. These rules were, however, diver-se, and, as a result, cooperation at the internati-onal level was launched with the aim of harmoni-

sing and broadening the efforts targeted to pro-tection to as many countries as possible.Following various initiatives the adoption of the

Figure 3. The treasure of the wreck of the Nuestra Seorade Atocha at Mel Fisher Days (www.schoonerwharf.com)

Figure 4. Uluburun wreck - recovering ingots 1, 2(archaeologyhouston.wordpress.com)


1996 ICOMOS Charter on the Pro-tection and Management of theUnderwater Cultural Heritage cameas a major step forward. It was onthe basis of this charter that theUNESCO Convention on the Pro-tection of the Underwater CulturalHeritage was finally adopted in2001. This was followed by its ratifi-cation in some forty countries, ma-king this to date the most importantinternational achievement in thelegal protection of underwater heri-tage. This convention definesunderwater heritage as all traces ofhuman activity that possess a cultu-ral, historic or archaeological significance andthat were sunk at least 100 years ago. This hasset the legal grounds for the preservation of thisheritage at the global level.

THE CONVENTION

The 2001 UNESCO Convention on the Protecti-on of the Underwater Cultural Heritage aims tosee states afford better protection to theirunderwater heritage. The cornerstones of theConvention set out the basic principles for theprotection of cultural heritage, foresee a detailedsystem of cooperation among countries and es-tablish generally accepted rules for the treat-ment and research of underwater cultural herit-ge.

THE PRINCIPLES

The first principle is the obligation toprotect cultural heritage for the benefitof humanity. Accordingly, states parti-es to the Convention (signatories)should protect underwater heritage.Each state implements this protectionin accordance with its capabilities,

and if it is not able to undertake rese-arch of an archaeological site, it isenough that it provides appropriateprotection of the site. The Conventionencourages scientific research of sitesand public access.

PRESERVATION

The Convention considers the preservation ofunderwater cultural heritage at its original locati-on, on the seabed, the first option, having prece-dence over all others. Objects may be collectedif this serves to rescue them from unavoidabledestruction as a result of, for example, construc-tion work, or if collection constitutes a significantcontribution to the protection and research ofunderwater cultural heritage.

NO COMMERCIAL EXPLOITATION

The Convention establishes that there may beno commercial exploitation of underwater herita-ge for the purpose of trade. Finds may also notbe dispersed in a fashion that would preventtheir subsequent location. These provisions are

Figure 5. Uluburun wreck, reconstruction at Bodrum Museum(en.wikipedia.org)

Figure 6. The bow of the Titanic shipwreck (wavesnewsletter.com)


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in line with the moral principles applicable tocultural heritage on land and do not prevent ar-chaeological research or tourist visits to archae-ological sites.

TRAINING AND INFORMATION EXCHANGE

States parties to the Convention should promotethe exchange of information and the transfer of

technology with the aim of improving the protec-tion and research of underwater heritage. It alsoencourages the provision of training inunderwater archaeology and international coo-peration in the research, protection and mana-gement of underwater cultural property. It in par-ticular emphasises the need to raise publicawareness of the need to preserve underwaterheritage.

OTHER KEY PROVISIONS

The Convention does not determine theownership of individual finds and sites, nor doesit touch upon issues of state sovereignty anddeclares that it shall not contradict other interna-tional law, including UNCLOS, the United Nati-ons Convention on the Law of the Sea. Any sta-te may sign this convention, independent of

whether it is a party to any other convention.When adopting these principles the Conventionalso encourages ratifying countries to provideexplicit protection to the cultural heritage of in-land waters such as rivers and lakes. This pavesthe way for the participation of landlocked coun-tries in the overall goal of protecting underwaterheritage.

States parties are also to notify other countriesin the event of the discovery of a shipwreck inthe area of their exclusive economic zone or ininternational waters, with the aim of establishinga coordinating country that will take measures toprotect the site.

States parties shall train or develop their owncompetent bodies that will see to establishingand maintaining a list of underwater cultural heri-tage. These bodies will also secure the protecti-on, conservation, presentation and managementof underwater heritage and nurture study andeducation in this field.

Figure 7. Mary Rose 2005 excavation site recorder map(www.3hconsulting.com)

Figure 8. The stem of the Mary Rose is raised(www.3hconsulting.com)

Figure 9. Mary Rose painting (www.3hconsulting.com)


THE ANNEX

The adoption of the Convention was followed bythe adoption of the Annex to the Convention,which stipulates in greater detail the practicalaspects of the protection of underwater heritage.The Annex to the Convention sets out the rulesthat pertain to various activities directed atunderwater cultural heritage. These aregenerally accepted practical rules that are to beobserved during excavation, such as themethodology applied. It also establishes guideli-nes for how research projects and future preser-vation should be conceived. The Annex alsocites the qualifications researchers should pos-sess to undertake activities related to the pre-servation and management of underwater cultu-ral heritage. The rules contained in the Annexare one of the more important achievements ofthe Convention and it is felt that every professio-nal working in the field of underwaterarchaeology should strictly abide by them.

The Annex makes several references to the con-servation and restoration of finds. Rule 10, forexample, which determines project design, alsostipulates the obligation to draft a conservationprogramme for artefacts and the site in coopera-tion with the competent authorities. In the chap-ter dedicated to funding and project duration, inrules 17, 19, 20 and 21, there is specific mentionof the need to draft a contingency plan for fun-

ding and time required for conservation even inthe event of the termination of the project or aninterruption of expected funding. Of particularimportance is chapter VIII of the Annex, rules 24and 25, which detail conservation programmesfor small finds and features during research,transport and the long - term storage of finds.

IMPLEMENTING THE CONVENTION

The supreme body of the Convention is the Me-eting of States Parties, convened at least onceevery two years. Expert and advisory support tomember states is provided by the Scientific andTechnical Advisory Body (STAB), which poolssome ten top experts in the field of underwaterarchaeology. Ad hoc States Parties WorkingGroups may also be established to discuss,among a limited number of participants, issuesand to prepare working materials for Meetings ofStates Parties. The organisation and coordinati-on of these bodies and similar tasks is carriedout by UNESCO, the Director-General and theConvention Secretariat based in Paris.

Figure 10. Mrs Irina Bokova addresing the 2011 Sessionof the UNESCO 2001 Convention State Parties in Paris(Photo: L. Beki5)

Figure 11. Vasa Museum Interior (traveling-kids.blogspot.com)

Figure 12. Vasa Museum Exterior (it.wikipedia.org)


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CONCLUSION

From the beginnings of underwater research tothe present day there has always been greatpublic interest for underwater cultural heritage.In the past souvenirs were collected fromshipwrecks, there were exciting articles in thepress, and many television and feature length

films have been made on expeditions seekingnew underwater discoveries.

The number of specialised museums that exhibitrestored and conserved underwater finds andeven small vessels extracted from the seabedhas now grown. Noteworthy are Sweden's VasaMuseum, visited every year by three quarters ofa million people, the museum at Bodrum inTurkey, the museum housing the once sunkenwarship Mary Rose in Great Britain and manymore. Improvements in diving techniques andequipment has seen a growth in the number oftourist divers who make organised visits tounderwater archaeological sites.

Underwater archaeological parks have beenestablished where sunken architectural remainscan be viewed, such as the Roman period portof Caesarea in Israel and the National MarineProtection Area in the Bay of Pozzuoli in Italy.Much more numerous, however, are thefrequently visited locations of shipwrecks suchas the Florida Keys Marine Sanctuary with seve-

ral shipwrecks, the wreck of the Yongala in Aus-tralia and the wreck of the Baron Gautsch inCroatia. Organised visits to underwater sites arein line with the guidelines of the Convention,which give preference to the in situ protection ofunderwater heritage, and it is to be expectedthat there will be a growing number ofunderwater sites rendered accessible to visits bydivers.

It should, therefore, be in everyone's interest toprotect underwater cultural heritage with the aimof preserving it for future generations, and todevelop the economic and tourism potential thatmay emerge from its proper care.

This legal framework, which protects underwaterheritage, must be adhered to at the national le-vel, which, besides the adoption of the appropri-ate laws and regulations, implies practical worktargeted to protection. Above all this pertains topeople involved in the protection and researchof this heritage at the actual sites, most of whoare underwater archaeologists. Other people notactive in the systems of protection also comeinto contact with these locations. These are,above all, divers - professionals involved in trai-ning and guiding recreational divers. Nationalbodies, such as the maritime police, the portauthorities, coast guard and others who, as aresult of their competences, may play a key rolein the protection of archaeological sites, alsoneed to be included in the system of on - siteprotection.

Another key aspect - one that is,unfortunately, often overseen - isthe protection of objects extractedfrom the water for the purpose ofresearch. Early efforts to collectand research sunken objects didnot give much heed to the conser-vation and restoration of the ob-jects extracted from the water.Consequently they were damagedor often entirely destroyed as aresult of an abrupt change to theenvironment in which they weresituated. This has seen countlessvery valuable finds collected in theFigure 13. Baron Gautsch wreck (Drawing: D. Frka; www.rovinj-online.net)


past century irretrievably lost, despite being keptin various collections and museum depots.

In recent decades some restorers and conserva-tors of archaeological finds have taken an inte-rest in specialising in the protection of objectscollected in wet environments and in developingvarious procedures and technologies to protectthem.

The Underwater Archaeological Finds Restorati-on and Conservation Department in Zadar, Cro-atia was founded in 2007. It is now a part of In-ternational Centre for Underwater Archaeologyin Zadar, a UNESCO category II centre. Conser-vation workshop pools a diverse team ofexperienced conservators - restorers and che-mists who have specialised in treatingunderwater finds. This handbook is their work

and in it, in a concise fashion, they have endea-voured to outline to those interested the met-hods whereby various types of objects are pro-tected. This work is largely based on their wealthof practical experience, and on a synthesis ofnumerous expert papers on the subject fromaround the world.

Figure 14. Caesarea location 14 (www.caesarea-diving.com)

Figure 15. Caesarea visitor's map (www.caesarea-diving.com)


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INTRODUCTION

The protection of artistic heritage is as old as thehistory of our civilisation. It is a complex processthat involves human activity and the will to pre-serve artistic heritage from destruction or loss.The preservation of objects of archaeologicalheritage is the chief goal of conservation andrestoration work. Conservation and restoration isa lengthy process that often requires significantfinancial resources. It consists of a series of pro-cedures, methods and interventions that preventthe further deterioration of objects, and restorestheir physical integrity and visual identity.

Without the implementation of conservation andrestoration interventions most artefacts woulddecay, and the historic and artistic data wouldbe forever lost.

In their work every conservator - restorer shouldadhere to the Professional Guidelines & Code ofEthics. The Code of Ethics establishes the termsof reference and the definition of the conservator- restorer's profession as confirmed and broade-ned at the general assembly of the EuropeanConfederation of Conservator - Restorers Orga-nisations (ECCO) held in Brussels in 1993. Thesecond version of the Professional Guidelineswas adopted at the Brussels general assembly

on 1 March 2002, while the second version ofthe Code of Ethics was adopted at the generalassembly held in Brussels on 7 March 2003.

PROFESSIONAL GUIDELINES

The objects, buildings and environments towhich society attributes particular aesthetic, arti-stic, documentary, environmental, historic, sci-

entific, social, or spiritual value are commonlydesignated "cultural heritage" and constitute amaterial and cultural patrimony to be passed on

to coming generations.By definition the conservator - restorer is a pro-fessional who has the training, knowledge, skills,experience and understanding to act with theaim of preserving cultural heritage for the future.The fundamental role of the conservator-restoreris the preservation of cultural heritage for thebenefit of present and future generations. Theconservator - restorer carries out diagnosticexamination, conservation - restoration treat-ment of cultural property and the documentationof all interventions. Diagnostic examination con-sists of the research of relevant existing informa-tion; the identification and determination of thecomposition and the condition of cultural herita-ge; the identification of the nature and extent ofalterations and an evaluation of the causes ofdeterioration. Conservation consists mainly ofdirect action carried out on cultural heritage withthe aim of stabilising its condition and retardingfurther deterioration, while restoration consists ofdirect action carried out on damaged or deterio-rated cultural heritage with the aim of facilitatingits perception, appreciation and understanding,while respecting as far as possible its aesthetic,historic and physical properties. Documentationconsists of an accurate pictorial and written re-cord of all procedures carried out and the resul-ting insight. Recommendations regarding stora-ge, maintenance, display or access to cultural

heritage should be specified in this documentati-on.

Furthermore, it is within the conservator -restorer's competence to: develop programmes,projects and surveys in the field of conservation- restoration; provide advice and technical assis-tance for the preservation of cultural heritage;prepare technical reports on cultural heritage;conduct research; develop educational program-

II. Guidelines, Ethics and the Methodology ofConservation - Restoration Work

Mladen Musta7ek

[email protected]

Musta7ek M.: Guidelines, Ethics and the Methodology of Conservation - Restoration Work 15

mes and teach; disseminate information gainedfrom examination, treatment or research; promo-te a deeper understanding of the field of conser-vation - restoration. As the primary aim of con-servation-restoration is the preservation of cultu-ral heritage, it is distinct from art and crafts. Theconservator - restorer is distinguished from otherprofessionals by her/his specific education inconservation - restoration.

THE CODE OF ETHICS

Every conservator - restorer should adhere tothe principles, obligations and rules of behaviourembodied in the code of ethics in the practice oftheir profession. As the profession of conserva-tor - restorer constitutes an activity of public inte-rest, it must be practised in observance of allpertinent national and European laws and agre-ements. The conservator - restorer worksdirectly on cultural heritage and is personallyresponsible to the owner, to the heritage and tosociety. Failure to observe the principles, obliga-

tions and prohibitions of the Code constitutesunprofessional practice and will bring the profes-sion into disrepute. In their work conservator -restorers contribute to a better understanding ofcultural property, mindful of its aesthetic, historicand spiritual significance and its physicalintegrity. By his or her knowledge of the materialaspects of objects possessing historic and artis-tic significant, the conservator - restorer pre-vents their deterioration and increases thecapacity of comprehension by emphasizing thedifference between what is original and whathas been replaced. In their work conservator -restorers must adhere to the highest standardsof the profession regardless of the market value

of the cultural heritage. All aspects of preventiveconservation should be taken into account befo-re carrying out interventions directly to culturalheritage so that the conservator - restorer maylimit the treatment to only that which isnecessary. The materials used by the conserva-tor - restorer should be compatible with the ma-terials of the cultural heritage and as completelyreversible as possible. Every conservation - res-toration treatment of cultural heritage should bedocumented, and the report should include

written and pictorial records of all conservation -restoration interventions and diagnosticexamination with the names of all those whohave carried out the work. The conservator -restorer must strive to enrich her/his knowledgeand skills and cooperate and exchange informa-tion with other professionals with the constantaim of improving the quality of her/his professio-nal work.

THE METHODOLOGYOF CONSERVATION ANDRESTORATION WORK

When initiating conservation - restoration workwe must first undertake the careful examinationof the object in question and its context. Theobject must be carefully studied in order to pro-duce as appropriate as possible a determinationof what to do and how it should be done. In or-der to gain the most proper and confidentknowledge of the archaeological object understudy a conservator - restorer may, during the

examination, undertake scientific analysis andspecial surveys. The study of the archaeologicalobject should yield insight into the kind of mate-rials and techniques used and the intentionsinherent in the object's manufacture. Alterationsthat an object has been subjected to over timeshould also be ascertained. Respectful of theintegral object and of its history and context, theconservator - restorer shall critically assesswhich alterations act as disfiguring factors,which should - with the aim of facilitating theperception, appreciation and comprehension ofthe cultural heritage - be removed, and whichchanges are an alteration of the original materialthat it would be a mistake to eliminate (VOKI4

2007, 261).

The real or potential value of cultural propertymay be destroyed by conservation - restorationinterventions. In order to avoid this the value ofcultural property must be assessed and recogni-zed. In order to define a proposal of actions andthe order in which they are to be conducted, theconservator - restorer must establish thefollowing: the nature of the original material and


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the production technique applied; what changesto the material and which additions to the materi-al have occurred as a consequence of the pas-sage of time; which changes are a disfiguringfactor and which are acceptable; what are thereasons for undertaking the intervention on theobject; what is the entirety of the object and itscontext; what was the history of the object, whatwere the intentions of its author and what value

is inherent to the object (VOKI42007, 262).The determination of the method in which con-servation - restoration work is to be conducted isfollowed by the selection of materials and proce-dures to be applied. Materials and proceduresare determined for each phase of conservation -restoration work. The following principles are tobe respected in the selection of materials andprocedures: the principle of minimal necessaryintervention; the principle of visual and structuralcompatibility of the materials and proceduresapplied with the original materials and originaltechniques of manufacture; the principle of thereversibility of the materials and procedures ap-plied; the principle of the distinctness of the in-tervention and the principle of sustainability(VOKI42007, 263). The professional guidelinesdivide the concept of preservation into the termspreventive conservation and remedial conserva-tion (PEDII42005, 12). The preventive conser-vation of an object of cultural heritage consistsof indirect actions, while remedial conservationconsists of direct action on the cultural property.Restoration involves direct action on culturalproperty that is deteriorating or has been dama-ged, with the aim of facilitating the understan-ding of the cultural property. To reduce directintervention on cultural property to the smallestpossible measure the conservator - restorermust take into consideration all preventive con-

servation options when determining restorationprocedures.

Written records and photographic documentati-on based on a defined system must be kept du-ring conservation - restoration work. This systemis known as conservation - restoration documen-tation; it is an integral part of the cultural herita-ge and must be accessible. Conservation - res-toration documentation has as its goal: to provi-

de for and secure a methodological approach toconservation - restoration work; to establish theintention and value contained in the cultural heri-tage; to determine the material to be preservedand changes that have occurred (VOKI42007,258). Conservation - restoration documentationshould include: inventory data that establishesthe heritage in question, research documentati-on, work proposal drafts, the documentation of

conservation - restoration work, instructions forthe method of preservation and maintenanceand photographic records of the appearanceand condition in all phases prior to and after theintervention (VOKI42007, 259).

5. CONCLUSION

The responsibility and the gradations of the workof a conservator - restorer are established by theCode of Ethics. Given that conservator - resto-rers work with historic originals, which possessartistic, religious, scientific, cultural, social andeconomic value, the conservator - restorer has

particular responsibility for the preservation oftheir physical integrity. The professional guideli-nes establish the fundamental role of the con-servator - restorer as being the preservation ofcultural heritage for the benefit of present andfuture generations, and to contribute to a betterunderstanding of its aesthetic and historic attri-butes (PEDII42005, 12). According to the co-de of ethics the work of the conservator - resto-rer encompasses the technical examination,preservation and conservation - restoration ofworks of art. When undertaking restoration pro-cedures the conservator - restorer should alsoendeavour to apply those products, materialsand procedures that will not have a negativeeffect on the work of art. Restoration documen-tation must contain all relevant data related tothe procedures conducted on the culturalproperty. This restoration documentation beco-mes a part of the work of art, also as determinedby the professional guidelines (PEDII4 2005,13).

Musta7ek M.: Causes of the Decay of Archaeological Material 17

INTRODUCTION

Like other materials in the natural environment,underwater archaeological material is exposedover time to the effects of its environment and is,as such, subject to change. There are numerousand diverse physico - chemical reactions thatare referred to as natural aging. The dynamicsof these reactions affects the quality anddurability of a material. The process of deteriora-tion is a natural one and its speed varies for ea-ch material (MUNJAK 2008, 132). The natureof the substance from which the archaeologicalmaterial is made and the microclimatic environ-ment in which it is situated affects the deteriora-

tion of the archaeological material. Some typesof macro and microorganisms find a suitablehabitat for their development on objects of ar-chaeological heritage. The living species thatinhabit these materials range from microscopicbacterial cells to plants and animals (TIANO2010, 1).

In long term exposure to a given set of conditi-ons a material will tend to achieve a state ofequilibrium with the environment in which it isdeposited. And while it may be slow, the deterio-ration of archaeological material is inevitable.The extraction of archaeological material from amarine environment leads to a change in theprimary microclimatic environment, and upsetsthe state of balance established between thematerial and its environment. Atmospheric ef-fects begin to act upon the material that encou-rage and accelerate numerous decompositionprocesses. The timely conduct of appropriateconservation procedures is, therefore,necessary with the objective of stabilising theartefact, retarding the further deterioration of thematerial, and of ensuring its safekeeping untilconservation procedures can be undertaken.

The environmental factors that can affect boththe deterioration and the preservation of an arte-fact are: physico - chemical, biological and mec-hanical.

PHYSICO - CHEMICAL CAUSES OFDAMAGE

WATER

Water is a complex medium consisting of purewater, mineral salts, dissolved gases and microand macroorganisms (MEMET, 2007, 153).Water is known as the universal catalyst as itactivates other causative agents of deterioration,facilitates and accelerates most chemical reacti-ons and allows organisms to develop. Submer-ged artefacts may be damaged by the activity ofother components besides pure water, such assalts, dissolved gases, organic substances andundissolved particles.

The physic - chemical action of water onunderwater artefacts causes various types ofdamage. Water causes ceramic, stone andglass objects to become saturated with the saltspresent, which leads to the weakening of thematerial's structure, delamination and the dama-ging of the surface of the material. The effect ofwater on objects made of metal encourages thedevelopment of a very intensive process of cor-rosion that destroys the metal structure of theobject and irreparably damages it. Artefacts ma-de of wood and other organic materials are most

sensitive to the action of water. Besides the factthat water is the chief agent of biodegradation, italso penetrates the organic structure of the ob-ject causing the weakening of the organic struc-ture of the object. Many organic materials conta-in water in the structure of their fibres and cellsthat is balanced with the surrounding atmosphe-re.

When they are exposed to a drier or wetter envi-

III. Causes of the Decay of ArchaeologicalMaterial

Mladen Musta7ek

[email protected]


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ronment they are deformed (shrink or swell),whereby the original form of the object is lost.

SALTS

Salts are ionic bonds created by a reactionbetween an acid and a base. When dissolved,salts split into individual ions, calcium (Ca2+),bicarbonate (HCO3-), sodium (Na+) and chloride

(Cl-

). Unlike soil and internal waters, mostseawater contains soluble salts. The chief ionspresent in seawater are Na+ and Cl-, and thelevel of SO42-is also high.

Salinity, i.e. the total mass of dissolved salt, isnot the same in all marine environments anddiffers based on geographic area. The averagesalinity of global seas is 35, while the salinityof the Adriatic Sea is 38. All salts are solubleto a certain degree, but the solubility of some isnegligibly small, and we refer to these salts asinsoluble. Salts of relatively high solubility are:nitrates, chlorides, sulphates, bicarbonates andacetates, while those of low solubility are silica-tes, oxides, sulphides, phosphates and carbona-tes. Other factors, such as pH value, also affectsolubility. Carbonates, oxides and sulphites are

more soluble at low pH levels, while silicates aremore soluble at higher pH levels. Salts dissolvedin seawater contribute to the formation of a cor-rosive environment as they act as electrolytesthat accelerate the electrochemical corrosion ofmetals, leading to their decomposition (MEMET,2007, 152).

Soluble salts on porous archaeological material

such as ceramics and stone may cause signifi-cant damage, especially upon being brought upto the surface. Artefacts extracted from the seamust be kept submerged in water until the desa-lination process; otherwise the evaporation ofwater could lead to the crystallisation of solublesalts, increasing their volume and the fracturingof the structure of the material.

Upon extraction to the surface underwater arte-facts are exposed to atmospheric influences thatalso contain soluble salts. Large quantities ofNa+ and Cl- can be created from seawater orsalt saturated aerosol (windborne seawater).Particular attention should be given to this fact ifthe underwater artefact is exposed in an openarea that is not protected from atmospheric influ-ences. Salt in the air in combination withhumidity and other compounds and particles inthe air create electrolytes on metals that facilita-te electrochemical corrosion and the deteriorati-on of metals (SCOTT, EGGERT, 2009, 109).Soluble salts in the atmosphere are most oftendeposited on the surface of materials. Surfacedamage caused by deposits is most frequent inceramics and stone, but other porous materialsare also subject to damage caused by solublesalts (CRONYN 1990, 23). Like soluble salts,insoluble salts may form deposits on any arte-fact. The exposure of material to the effects ofinsoluble salts usually causes surface damage

and changes in the colour of materials.

OXYGEN

The presence or absence of oxygen is the chiefcontrolling factor in the activity of organisms thatcause the decomposition and deterioration ofarchaeological material. Oxygen is a componentof many chemical reactions that directly orindirectly lead to the damaging of material. A

Cations (g/L) Anions (g/L)

Na+ 11.04 Cl- 19.88Mg2+ 1.30 SO42- 2.74Ca2+ 0.42 HCO3- 0.18K+ 0.39 Br- 0.07Sr+ 0.008 F- 0.015

Origin Salinity ()Rivers (mean world

value) 0.1Baltic Sea


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to the survival of fouling organisms, which have

a much more detrimental effect on materials.The effects of light on underwater artefacts aremore significant in a dry environment where di-rect exposure to UV radiation can cause detri-mental changes to materials. Artificial sources oflight - common light bulbs, halogen wolframbulbs and fluorescent bulbs - also emit UV andheat radiation. To reduce their detrimental ef-fects they must be covered with special protecti-ve films with UV filters (SCHAEFFER, 2001, 26).Damage from direct exposure to UV radiationdepends on the sensitivity of individual types ofmaterial. UV radiation can cause the bleachingof the surface of an object, the weakening andfracturing of the structure and cause it to fallapart. The inorganic materials ceramic, stone,glass and metal have a low level of sensitivity toUV radiation, while pigments and organic materi-als such as wood, textile and leather are muchmore sensitive to UV radiation, and paper is verysensitive. UV radiation can also damage protec-tive coatings such as resins and lacquers onalready conserved and restored artefacts, whichmay activate deterioration process in the materi-al. IR radiation on archaeological material cau-ses it to heat up.

All sources of light cause a certain amount ofheating. An increase in temperature impacts therelative humidity in the air and the percentage ofhumidity of the artefact. Heating caused by artifi-

cial sources of light cause drying and an elevati-on of temperature that accelerates the processof the decomposition of material. The recom-mended maximum value of light exposure forhighly sensitive material such as textile, leatherand paper is 50 lux. Materials with moderatesensitivity such as wood, bone, and materialswith a protective coating such as resin andlacquers have a maximum recommendedexposure value of 150 lux, while artefacts of me-

tal, ceramic, stone and glass, in spite of their low

sensitivity to light have a maximum recommen-ded exposure value of 300 lux.

POLLUTED AIR

By its composition air is a mixture of gases. Itscomposition changes depending on geographicposition and in its natural state it contains a cer-tain percentage of water vapour. Along with thenormal gases, air may also contain some othergaseous and solid matter we refer to as atmosp-heric contaminants. Gases such as sulphur andnitric oxides, carbon monoxide and dioxide,chlorine, hydrogen peroxide, hydrogen sulphideand others cause air pollution. Polluted air mayalso contain large quantities of water vapour,smoke and dust. Smoke in the air may originatefrom the incomplete burning of wood, naturalgas and petroleum derivatives or coal. Smokecontains tar substances that can accumulate onthe surfaces of objects over time, creating asticky mass of brown or black colour, thus impai-ring the aesthetic aspect of the object.

There are three chief sources of contaminatedair that can have a detrimental effect on archae-ological objects:

The external environment, which produ-ces dust and atmospheric contaminants;

The environment in a museum or depot

which may be exposed to dust or conta-minants created by restoration work inworkshops;

Materials used for storage or theexhibition of objects that may contain har-mful chemicals.

Elements of atmospheric pollution can causedetrimental chemical reactions on almost alltypes of material (VAN GRIEKEN, DELALIEUX,

Table 3. The electromagnetic spectrum


GYSELS, 1998, 2327). On organic material at-mospheric pollution can lead to elevated acidityand the weakening of the structure of materials.On metal objects atmospheric pollution can in-duce detrimental corrosion processes, while onceramic and stone objects it can lead to the stai-ning and bleaching of surface areas and chan-ges in the colour of the object.

THE BIOLOGICAL CAUSES OFDAMAGE

FOULING ORGANISMS

The biological causal agents of the decay ofunderwater artefacts are fouling organisms,which we can divide into micro fouling organi-sms and macro fouling organisms. Fouling orga-nisms are animals and plants that are a compo-nent part of marine, river and lake biomasses.Micro fouling organisms such as bacteria andalgae have a detrimental impact on materials inan underwater environment, while in dry envi-

ronments, besides bacteria, moulds, fungi andlichens. Numbered among the macro foulingorganisms in underwater environments are: co-rals (Anthozoa); molluscs (Mollusca); polychaeta(Polychaeta); crustaceans (Crustacea); echino-derms (Echinodermata) and fish (Pisces), whilein dry environments they include insects androdents. Fouling organisms inhabit almost alltypes of archaeological materials, with theexception, for example, of objects made of cop-per and bronze on which, because of their biolo-

gical toxicity, the phenomenon is less prevalent(MEMET, 2007, 164).

The appearance of a given fouling organism onarchaeological artefacts depends on variousfactors, such as temperature and salinity values,the concentration and saturation of oxygen andthe type and amount of time the material hasbeen submerged. Fouling organisms on archae-

ological material causes various kinds of dama-ge. Macroorganisms, such as molluscs, usuallycause physical damage to archaeological mate-rial, in particular wood and other organic materi-als, while microorganisms encourage corrosionprocesses on metal and are the chief causalagent of the effect of biological decompositionthat causes surface damage and the weakeningof the structure of materials. When the life cycleof fouling organisms on colonised artefactsends, their remains are deposited and limestoneand other sedimentary rock form organogenicsediments on materials (ESTANOVI4 1997,115). The formation of sediments on artefactsleads to the creation of a local microenvironmentthat protects the material from direct exposure tothe environment and further accelerated decay.In these isolated environments the process ofdecomposition is retarded. Sedimentation is theonly natural process that provides for the partialpreservation of iron finds, which, if directlyexposed to the activity of the sea, wouldcompletely erode and decay (SCOTT, EGGERT,2009, 123).

MICROORGANISMS

Microorganisms are primitive organisms verysensitive to the environment. They are also notresistant to high levels of salts and the toxic pro-ducts of copper corrosion and certain organic

chemicals. Some kinds of microorganisms haveadapted and are resistant to extreme pH levels,desiccation and oxygen deficiency. The metabo-lism of microorganisms is not particularly effecti-ve and, instead of carbon dioxide, they secreteorganic acids. Individual microorganisms are notvisible to the naked eye, but their colonies are(CRONYN 1990, 15). The effects of these orga-nisms on materials, known as biodegradation,are most evident in organic materials and are

Figure 1. Object covered by organogenic sediment(Photo: M. Musta7ek)


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part of the natural cycle of decay. The effects ofthe waste by - products of the metabolic proces-ses of microorganisms such as organic acids onarchaeological material may cause chemicalweakening and accelerate its decay. The appea-rance of an artefact may also be visually deterio-rated by pigment particles created by mycelium,bacteria or black sulphide created by the activityof anaerobic sulphate reducing bacteria, while

the surface of an object covered in microorgani-sms may be unrecognisable.

ALGAE

Algae are a broad group of simple, mostly waterinhabiting, photosynthesizing organisms(ranging from unicellular to multicellular) similarto plants. Algae are able to live in neutral toweakly alkaline environments, in extremes oftemperature and salinity, and in environmentsranging from total darkness to sufficient light.Algae are divided into seven classes, and colourof algae varies from red to dark purple, which isthe result of a mixture of various pigments. Thenames of individual divisions and classes of al-gae are derived from their colour. A commontrait of all algae is photosynthesis, which produ-ces oxygen as a by-product and supplies it toaqueous environments. In relation to the sub-strate they inhabit we can divide algae into twogroups: epilithic algae, which grow on the surfa-ce of the substrate; and endolithic algae, whichpenetrate and colonise the interior of the sub-strate (KUMAR, KUMAR 1999, 18).

Algae can influence the deterioration of archae-ological material by causing physical and chemi-cal damage. The effect of algae on archaeologi-cal objects is usually the loss of aesthetic value.And while the direct damage to material causedby algae is not always significant, they indirectlyinfluence the deterioration of materials by sup-

porting the growth of biological causes of corro-sion such as moulds and lichens (KUMAR, KU-MAR 1999, 19). Algae may also cause biodegra-dation. They produce various metabolites, forthe most part organic acids, which have an acti-ve effect on materials causing their decay andpermanent damage.

BACTERIA

Bacteria are single - celled microorganisms, andthe single largest group of life forms. They areinvisible to the naked eye, propagate quicklyand can form colonies of several million units inthe space of a few hours. Their size ranges fromone to several microns. In unfavourable conditi-ons bacteria create special, very resistant cells -spores, which they can also use to multiply.Spores are very robust: they can endure longdrought, various chemicals and both high andlow temperatures (MUNJAK 2008, 138). Bacte-ria use enzymes to break down organic substan-ces they use as food.

The effects of bacteria on archaeological materi-al may lead to permanent damage caused bythe degradation and decomposition of materials.When present on an artefact in greater numbersbacteria appear in the form of coloured blemis-hes, since many of them create particles of pig-ment, incrustations and black sediment. Bacteriasecrete enzymes that decompose organic sub-strates and , like fungi, are aerobic. There is astrain of bacteria that are anaerobic and that,

Figure 2. The algae covered barrel of a bronze cannon(Photo: M. Musta7ek)

Figure 3. Black sediment created by the decay anddecomposition of iron (Photo: M. Musta7ek)


unlike other organisms, do not require oxygenfor respiration. They secure nourishment by thereduction of inorganic chemicals such as nitra-tes, carbon dioxide, manganese (IV) and iron(III). This method of respiration is inefficient andineffective and as a result bacteria secrete orga-nic acids instead of carbon dioxide, which me-ans that they are able to colonise anoxic depo-sits. A number of these bacteria cause the des-

truction of organic artefacts, while some have anindirect effect on organic and inorganic materi-als. Noteworthy among these are anaerobic sul-phate reducing bacteria (SRB) such as Desul-phovibrio, which reduces sulphate to sulphide.The presence and activity of these bacteria indi-cate the danger of salt efflorescences and acidattack of the object after its drying. It can be de-termined by the odour of rotten eggs (hydrogensulphide) and the blackening of deposits causedby the formation of metal sulphides (CRONYN1990, 17).

MOULDS

Moulds are multicellular organisms of plant ori-gin at a higher level of development than bacte-ria. Moulds may be brilliantly coloured, black orwhite - depending on the species. They are re-cognisable as white, green, red or black blemis-hes of circular form, and from the odour of mo-uld. Active mould appears dirty or slimy. Dor-mant mould is dry, like talc. Moulds are unableto assimilate carbon from the air and live as pa-rasites on other organisms. Moulds reproducethrough spores or by the fragmentation ofmycelium. Mould spores are created in favoura-ble conditions in four to seven days. Mould spo-res are light and, like bacteria, they can remainairborne over great distances. In ver y unfavoura-ble conditions moulds may lay dormant for

years, and are very quickly activated in favoura-ble conditions. Mould mycelium die off quickly inunfavourable conditions, while their spores sur-vive. Special disinfection compounds arerequired to destroy them (MUNJAK 2008, 139).Moulds are able to colonise various types of ma-terial and may cause damage not only towooden surfaces, but also to paper, glue, leat-her, textile and other materials, especially in thepresence of relatively high levels of moisture

and heat, while some species may also have adetrimental effect on health (UNGER,SCHNIEWIND, UNGER 2001, 108).

FUNGI

Fungi are numbered among the most detrimen-tal of organisms responsible for the biodegrada-tion of organic and inorganic materials. The me-

tabolic diversity of this group of microorganismsincreases their ability to colonise various typesof substrate (wood, glass, stone). Fungi are for-med of a vegetative filamentous body ofmycelium, composed of series of identical cellscalled hyphae, and a reproductive system calledthe fruiting body. Spores develop in the fruitingbody that, in ideal conditions for growth, createnew hyphae cells. There are certain physical,chemical and biological conditions necessary forthe growth of fungi such as temperature, moistu-re, light, the presence of oxygen, the pH value ofthe substrate, and the type of material, whichhave different effects on the development of cer-tain types of fungi.

The fungi that cause the decay of organic mate-rial can be divided into two groups: fungi thatcause staining (stain fungi) and fungi that causedecomposition/rotting (rot fungi). Staining fungido not directly degrade cell walls and do norcause a significant reduction in their sturdiness,while rot-causing fungi attack the primary com-ponents of the material's cell wall, causing chan-ges in chemical, mechanical and physical traits(LIPANOVI4 2009, 2). A high percentage ofhumidity and an environment saturated withwater are the optimal conditions for the appea-rance of soft rot fungi, which attack thesecondary components of cell walls andcompletely destroy them (ARROYO, 2009, 42).

LICHENS

Lichens are multicellular composite organismsthat are formed by the symbiotic association oftwo plant organisms - fungi and algae. Thissymbiotic relationship allows them to survive inextremely dry and wet environments. They differgreatly in colour and shape, and their appearan-ce depends for the most part on the structure of


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the fungi. Lichens are the best known of theepiphyte plants. As individual organisms theyare aerobic and secrete a significant quantity oforganic acids (CRONYN 1990, 16). Their stratifi-ed structure guarantees lichens a long life spaneven after years of drought. A small number oflichens live in waters and seas. Lichens arehighly sensitive to air contaminants, especiallyto industrial pollution high in carbon dioxide. Lic-hens reproduce by producing spores. They arereleased into the air to find the right algae in or-der to establish a new symbiosis.

Lichens can affect archaeological heritage ob-jects both physically and chemically. Physicaldamage occurs by the penetration of hyphaeinto pores and the expansion and contraction ofthe thallus resulting from changes in moisture, inthe process of which there is damage to the sur-face of the object causing the formation of pitsand holes (KUMAR, KUMAR 1999, 22). Lichenscause chemical damage to archaeological mate-rial by secreting organic acids. They have a cor-rosive effect on the substrate created by the re-lease of metabolite acids. Metabolite acids cau-se chemical damage to the material by breakingdown and disintegrating the substrate.

MACROORGANISMS

Macroorganisms such as animals and plantsrequire oxygen for respiration and as such can-not function in an environment lacking oxygen.In order to survive all organisms require water insome degree. Organisms are not resistant todesiccation, extreme cold or heat. Noteworthyamong the living communities in the seas arecorals (Anthozoa); molluscs (Mollusca); bristleworms (Polychaeta); crustaceans (Crustacea);echinoderms (Echinodermata) and fish (Pisces).

These macroorganisms most often causephysical damage to archaeological material. So-me molluscs, for example, can bore canals intowood and stone, causing stains, fading and theporosity of the material. Major damage towooden objects in the sea is caused by theshipworm (Teredo navalis). It belongs to a groupof molluscs whose development depends on thesalinity and temperature of the water, such thata warm climate favours their development, while

cooler temperatures slow their activity. As theyuse wood as a source of food, they bore canalsinto it, in which calcareous depositsubsequently form (UNGER, SCHNIEWIND,UNGER 2001, 134). The actual boring of canalsinto wood weakens its structure, leading to thecracking and fracturing of wooden structures.Besides as a source of food organic and otherarchaeological materials may also provide a ha-bitat for some organisms.

MECHANICAL CAUSES OF DAMAGE

Mechanical damage to underwater archaeologi-cal heritage is caused by human and naturalfactors. The leading human factors affecting thedegradation of sites are: the non-professionalextraction and handling of objects, the looting ofarchaeological sites, find disturbance by divers,fishing activity (mussels, fishing nets), the an-choring of vessels, underwater constructionwork, waste dumping at sites and other factors.Numerous natural factors also cause damage tounderwater artefacts, such as sea currents,which, for example, carry sand and cause itsabrasive action against archaeological materialleading to extensive damage to the surface ofthe artefact, waves, various natural catastrophesand the accumulation of sediment.

Archaeological material, once deposited on theseafloor, riverbed of the bottom of a lake, isexposed to the inevitable accumulation of sedi-ment. Sediments that form over time subjectartefacts to significant pressure, which causesthe cracking and fracturing of the archaeologicalmaterial. The action of a strong sea currentshifts larger and heavier element of archaeologi-cal material and sediment, laying them on morefragile objects, which also leads to their crackingand fracturing. The speed of the sedimentationvaries significantly in individual environmentsand ranges from 1mm to several centimetres peryear. Sediments are very diverse and the vastmajority of seabed, riverbeds and lakebeds arecovered in them. The bottom contains the rema-ins of land erosion, mussels, the organic rema-ins of organisms and salts that have precipitatedfrom seawater. The sedimentary cycle includes


the erosion of rock, the transfer of substancesand the deposition of particles. Most of the ma-terial that is deposited in the sea comes by wayof rivers. These are either particles or dissolved.

There are three basic types of sediment in thesea:

Lithogenous particles that are transpor-ted to the sea by river, wind and ice andare created by the weathering of all typesof rock on land.

Hydrogenous are created by precipitati-on directly from a solution. Marine evapo-rites are created by deposition for themost part in semi-closed basins such ascoastal lagoons. Halite accounts for themajority of precipitated material.

Biogenous organisms create organo-gens. Biogenous sediments consist of theskeletal remains of organisms and of or-ganic substances. The majority of the cal-cium carbonate that is deposited in thesea is of biogenous origin.

CONCLUSION

An understanding of the mechanisms of the de-terioration of materials, combined with an under-standing of the factors that cause detrimentalchanges, is of exceptional importance. Agrowing number of analytical techniques havebecome available in recent decades that can be

applied to the study of the mechanisms of dete-rioration on various cultural heritage objects.Physico - chemical and biological factors suchas humidity, heat, light, bacteria, organisms andalgae are causes of deterioration that have adirect or indirect effect on materials, leading todetrimental changes. The speed at which a ma-terial achieves a state of equilibrium with its en-vironment is determined by the characteristics ofthe microclimatic environment. Climate is for themost part determined by temperature and therelative humidity (RH) of air. Materials graduallychange under the influence of environmentalfactors such as oxygen level, moisture and light.Organic materials such as bone, paper, textileand wood are subject, for example, to the split-ting or the polymerisation of molecules andoxidation. These chemical processes are acce-lerated by elevated temperatures - the higherthe temperature, the quicker the aging process.A high percentage of humidity accompanied byelevated temperature favours the developmentand growth of most biological destructive fac-tors. With an understanding of the mechanisms

of deterioration and timely acti-on taken to retard and preventthe further development of detri-mental processes on objects ofarchaeological heritage, we aremaking great strides with regardto safeguarding their physicalintegrity and long - term preser-vation.

Figure 4. A site covered by sediments (Photo: HRZ archives)


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INTRODUCTION

Ceramic finds are the most frequent atunderwater archaeological sites. The discoveryof ceramics profoundly changed the way peoplelived. Its permeability and durability provided forthe preservation, storage and transport of goo-ds, and changed human nutritional habits. Theprinciples of ceramic manufacture have remai-ned largely the same over time. It is based onthe modelling of earth, i.e. clay, followed by itsfiring at high temperature until a firm mass isachieved. Manufacturing techniques have beenperfected over time. It all started with the simplemanual shaping of a piece of clay, quicklyfollowed by the invention of the manual potter's

wheel, the fast potter's wheel, modelling by im-pressing the clay or pouring liquid clay into mo-ulds, the use of presses and so forth.

Unfired objects can be coated with white liquidclay and then engraved and/or decorated withvarious engobes or mineral pigments and thenfired. The glazes were applied and then fired forthe second time, which made the objects imper-meable to water.

Clays are formed by the alteration of feldspathicrocks under the influence of atmosphericagents: rain, rivers, winds and the release ofgases from the Earth's crust. Chemical reactions

turn feldspathic rock into kaolinite (Al2Si2O5(OH)4). If this process occurs within the rock itself, itis then possible to extract pure kaolinite from therock. Crushing this into a fine white powder pro-duces kaolin that, with quartz and calcite, is abasic component of porcelain. If this processoccurs on the surface of rocks, however, kaolini-te is mixed with organic materials, creating whatare known as white clays. The drainage of thesematerials and their accumulation at other sitescreate common clays, containing many impuriti-

es. After firing most take on a reddish colour asa result of the presence of a large quantity ofiron oxides. The chief characteristic of kaolinand clay is its plasticity or ability to retain defor-mation in spite of the absence of the force that

caused it.

Different substances are added to the clayprimarily to give the paste greater resistance, tosupport temperature changes during firing, toaccelerate drying, to decrease the retraction thatoccurs during drying, to reduce the plasticity ofthe paste and to lower the required firing tempe-rature. These substances include sand, quartz,plagioclase, potassium feldspar, rock fragments,powdered fragments of ceramics (grog), straw,feathers, shale, granulate slags or crushedshells (LOPEZ - ARCE 2013, 2031-2042). It isthese particles that are visible in the structure unique to every piece of pottery and the type

of clay used that are one of the means of diffe-rentiating ceramics. The porosity of ceramicsdepends on the extent to which the mineralshave been fused, the size of the particles of thecited tempers, and the quantity of organic mate-rials that will burn away at high temperaturesleaving cavities in their place. At lower firingtemperatures (800C) the individual mineraltemper grains are easily distinguishable from theclay matrix; at higher firing temperatures (1000-1050C) the sintering process produces an in-crease in the interconnection among these gra-ins and the matrix causing the porosity to decre-ase (LOPEZ - ARCE 2013, 2031-2042).

We can divide pottery into two major groups ba-sed on the firing temperature:

Ceramics fired at lower temperatures (fineand coarse unglazed pottery, glazedpottery, engobed pottery, majolica andother pottery fired at up to 1000 1200C)

Ceramics fired at higher temperatures(ceramics fired at above 1000 1400C,fire clay; soft - paste, bone china, hard -

IV. The Conservation and Restoration of Ceramicsand Pottery

Martina4urkovi5

[email protected]

4urkovi5M.: The Conservation and Restoration of Ceramics and Pottery 27

paste porcelain, stoneware)

In the first group we can include unglazedpottery dating from prehistory onwards, fired onopen bonfires or in primitive kilns that achievedtemperatures ranging from 500 to a maximum of700C, Roman period, medieval and all otherglazed and unglazed ceramics fired in closedkilns that achieved the appropriate temperaturefor firing ceramics of about 800 to 950C (e.g.

terra sigillata at 900 - 950C in an oxidation am-bient to achieve the bright red colour of the slip),and post medieval and other ceramics fired athigh temperatures that do not exceed 1000 -1200C. These may be objects with various ap-plied coatings or without, produced from com-mon red or white clay or some other commonclay.

We find examples of the second group in hardporcelain already in use during the early medie-val period (China, Korea, Japan), the soft-pasteand bone china in use since the 18th century(Europe), and the stoneware and fire clay thatare fired at very high temperatures ranging from

1000 - 1400C.

CERAMIC DETERIORATION

Degradation and alteration are natural pheno-mena in the lifetime of every material. It beginswhile the material is still in its original form, andcontinues in the forms humans have shaped itinto. The process is constant and unstoppable,and restorers can undertake a series of operati-ons on the object only in an attempt to slow theprocess. Alteration refers to the aging of objectsaccompanied by change that does not have adirect effect on the preservation of an object and

that does not impair its readability. This categoryof change includes alterations of colour, the for-mation of a superficial patina on objects and soforth. Degradation occurs as the advanced pro-cess of aging accompanied by a loss of theobject's readability.

The degradation of materials occurs as a resultof internal and external factors. The internal fac-tors are the characteristics of the material, of

which the greatest roles are played by porosityand capillarity. The external factors of degradati-on may be divided into two major groups: naturaland human. Marine environments are characte-rised by physical (abrasion, transport, depositi-on), chemical (dissolution - precipitation,oxidation - reduction) and biological (bacterial orbenthic organism growth) processes (LOPEZ -ARCE 2013, 2031-2042).

The degradation of materials is usually accelera-ted or activated when we remove the object fromthe environment in which it was deposited and inwhich it had achieved a state of equilibrium,even if imperfect, and we place it in another en-vironment. The most evident example of this isthe extraction of a find from an underwater envi-ronment in which it was conserved and quitestable for thousands of years, causing it to dryout in the air, leading to cracking and fracturing.We need to help these objects gradually adaptto the new conditions. The same happens withobjects deposited underground. Upon theirextraction from the site the objects are exposedto new conditions such light, changes in tempe-rature, changes in the level of humidity and con-tact with living organisms.

The chief natural factor leading to degradation iswater, which acts both as a physical and a che-mical factor, and is also a requisite for the pre-sence of biological factors. The physically des-tructive activity of water in the event of the free-zing of water in the pores of material is signifi-cant. The ice crystals formed have a volumemuch greater than that of water, which causesstress within the pore and leads to the crackingof the walls of the pore. The phenomenon ofrepeated freeze - thaw cycles lead to a loss inthe readability of the surface and finally to the

complete destruction of an object. Water is alsoa medium for soluble salts - the most frequentcause for the degradation of porous materialsextracted from the sea or environments close tothe sea. Seawater contains different types ofsalts, most prominently sodium, magnesium,calcium, potassium and strontium cations andchloride, sulphate, bromide and bicarbonate ani-ons (LOPEZ - ARCE 2013, 2031-2042).


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Over time objects submerged in seawater achie-ve equilibrium with the surrounding level of pres-sure, in the process of which air is released frompores and is replaced by salt water. At the mo-ment of the object's extraction from the sea andof the subsequent evaporation of water, the so-lution in the object becomes concentrated. Aftera time, when the solution becomes saturated,the process of salt crystallisation begins. Theformation of salt crystals has the same effect asthe process of forming ice crystals when waterfreezes. Their growth during formation causesstress within the structure of the object and thebreaking of bonds within the material itself.Slower evaporation of moisture from materialscauses salt crystals to break out to the surface -this is referred to as efflorescence. This pheno-menon is best observed when we remove a non-desalinized object from a moist environment andallow it to dry slowly in a cold place. We can ob-serve the formation of small white crystals onthe surface similar to fine hairs. This form of saltcrystallisation causes crumbling and sloughingfrom the object's surface. The speedier evapora-tion of moisture causes crystals to form insidethe object - this is referred to as subflorescence.The result is the cracking and fracturing of theobject. The phenomenon of the crystallisation ofsoluble salts is closely linked with the ambienttemperature, which determines the relativehumidity and the speed of water evaporation.

The composition and texture achieved with thefiring temperature is a key factor incrystallization decay and hence on the durabilityof these artefacts. Ceramics fired at higher tem-perature have lower surface area and less con-nected porosity, which entails a lower absorptionof soluble salts. Those fired at lower temperatu-re display lower total porosity but higher surface

area rendering them more prone to decay andless durable against weather. These materialsusually have more soluble salts and gypsumsubflorescence (LOPEZ - ARCE 2013, 2031-2042).

Ceramic archaeological finds from submarineenvironments are exposed to the accumulationof organic and calcareous deposits (insolublesalts), and the biochemical and physical effects

of living marine organisms. Algae has a bioche-mical effect as its secretions dissolve the sub-strate, while marine organisms such as snails,mussels, Cnidaria and polychaetous worms actmechanically upon ceramics, boring into themand scraping their surfaces (JAKI4, BIZJAK2010, 231-245). During their life cycles Crambecrambe sponges, encrusting sponges and theCliona sponge erode the surface of objects witha dense network of tiny holes visible after theirremoval. These surfaces are then fertile groundfor colonisation by lithophagous types of mus-sels such as the date mussel (Litophaga litopha-ga) and Gastrochaena dubia. We also find thecalcareous shells of polychaetous worms on thesurface of ceramic objects. Bristle worms belongto the genus Polychaeta and form calcareousshells in the form of a tube around their body.They are able to penetrate deep into porous ob-jects using their jaws or chemically with abrasion(JAKI4, BIZJAK 2010, 231-245). Accumulati-ons are also created by various types of Cnida-ria (the best known of which are various corals)and by green, brown and red algae.

We should also note the abrasive effect of thesea, which moves particles from the sea bottom(sand, pebbles) and in this fashion "sandblasts"and wears an object. Objects on the surface ofthe seabed are more exposed to abrasive actionthan those found under the surface. This abrasi-on leads to the rounding of the seams alongwhich fragmentation has occurred and the roun-ding of edges, and finally to the complete loss ofthe object.

Objects buried underground are exposed to thecirculation of waterborne minerals, causing theaccumulation of deposits on objects, most oftencalcareous, and possibly containing an

admixture of sand and soil. Siliceous depositsmay form, while the iron and manganese pre-sent in soil move to the surface and into porositi-es of the object, where they form brown blemis-hes (CAVARI 2007, 66).

The human effects on ceramics and stone ob-jects are also not negligible. These objects areworn while in use, but are particularly subject tothe consequences of indirect and unintentional


human influences. Human development is ac-companied by an increase in environmental pol-lution, which results in the formation of acid ra-ins, the accumulation of soot and other impuriti-es on cultural property, the pollution of seas bywaste waters and other effects. Anotherfrequent source of problems are the unprofessi-onal and obsolete previous attempts at restorati-on, which have not only failed to slow the pro-cess of deterioration, but have in fact often ac-celerated it.

THE CONSERVATION ANDRESTORATION OF CERAMICS

Conservation - restoration work on ceramic ob-jects can be divided into phases:

1. Initial documentation, prelimi nary analysis2. Cleaning the object3. Desalination4. Consolidation5. Bonding fragments6. Integration

7. Nuancing/retouching8. Drafting documentation after conductingrestoration work

In Figure 1. we can see that the sequence ofconservation - restoration work does not alwayshave to be the same. This depends on the stateof the object's preservation, the environment itoriginates from and the type and quantity of de-positions. The order of conservation - restorationinterventions may be changed and individualsteps may be skipped. In the case, for example,of a well - preserved vessel of firm structure, butin a fragmented state, we can immediately un-dertake the gluing of fragments without the priorconsolidation of the material. In some other ca-ses we will proceed in the opposite fashion, andwill undertake all necessary measures to preser-ve and strengthen the structure of the objectwhile any one of the following procedures maynot be required.

Conservation - restoration work also depends onthe final location and conditions in which theobject is to be stored (we cannot proceed fromthe same starting point if the object is to be keptin the open, such as at archaeological parks, orin a closed and controlled environment).

Any intervention will leave its trace and causestress to the object. It is, therefore, important tonote that all interventions on the object must beminimal to ensure that our actions do not causeeven greater damage to the object and to pre-serve the historic value of the object (the pre-sence, for example, of marine organism accu-mulations on the object bear witness to the siteat which the object was found, while organic andother remains tell of the object's use).

1. INITIAL DOCUMENTATION, PRELIMINARYANALYSIS

Documentation is the beginning and end of res-

toration work. The state of the object as it wasfound in situ or upon arrival at the laboratorymust be documented, as must all of the phasesof restoration work and the final appearancepost - restoration. We document every pheno-menon visible on the object, fractures, salt efflo-rescence, deformations, alterations to colour,loss of surface material, deposits accumulatedon the surface and all other forms of degradati-on and alteration, and observations concerningFigure 1. The phases of conservation - restoration work

(RAVANELLI, GUIDOTTI 2004,139)


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the object regarding decorations, reliefs and thelike. As a preliminary phase documentation hasan investigative role, and helps us discover theproblems related to the conservation of the ob-ject and to f ind soluti ons. It may be photograp-hic, written and drawn. Laboratory analysis andradiographic imaging of the object is also under-taken for documentation purposes and to revealproblem areas. As an example we can cite thesuccessful discovery of iron reinforcementswithin ceramic sculptures using radiographicimaging.

2. CLEANING

Cleaning is one of the most delicate phases inconservation - restoration work, followed by con-solidation, because both are for the most partirreversible, and as such require a goodknowledge and differentiation of foreign materi-als, i.e. accumulations and stains, from what areintegral parts of the object that require preserva-tion, such as patina, irregularities in manufactureand traces of use which should be left untouc-hed on the object.

Cleaning is done mechanically, mechanico-chemically, and chemically. We choose the me-ans based on the type of deposit accumulation,the state of conservation and the material ofwhich the object is made. In objects extractedfrom the sea we differentiate the calcareous andsiliceous deposits of marine organisms, the de-posits and infiltration of iron and copper oxidesand organic deposits (algae, sponges, bacteria).

It is recommended that any cleaning should be-

gin with most delicate techniques, such as brushdusting, cleaning with pads soaked in the mil-dest solutions such as distilled water or amixture of distilled water and alcohol and/or ace-tone. If these techniques do not help in remo-ving deposits and if the conservation status of afind allows it, we can apply slightly more aggres-sive cleaning techniques applying them in acontrolled manner and localised on the surfaceof the deposit. We must bear in mind that chemi-cal cleaning, although very effective and fasterthan mechanic cleaning, has some very signifi-cant drawbacks the process is not alwayseasy to control; the transport of dirty particles inpores is possible and it can leave soluble saltsin the interior of ceramics.

Removing calcareous andsiliceous deposits

Calcareous deposits are manifested in the formof the shells of mussels, the skeletal remains ofcorals, and as white spongy clusters that maycontain admixtures of sand and soil materials intheir structure. They are often closely merged tothe surface and are very hard. They can occurunderground by the deposition of calcium carbo-nate transported by water or in an underwaterenvironment as the result of the life cycle of ma-rine organisms inhabiting the walls of objects.We observe siliceous deposits as low, smoothwhitish - transparent accumulations. They arevery difficult to remove as they are practicallyfused with the surface of the object. They areremoved mechanically as siliceous bonds arevery resistant to chemicals and do not react tomild acids and bases.

Figure 2. Ceramic jug fouled by algae and the encrustations of marine organisms (Photo: M. 4urkovi5)


As the first choice, the mechanical removal ofdeposits is always suggested, whenever possib-le, from objects extracted from the sea whilethey are still wet and while the deposits have notbecome entirely petrified in contact with the air.Following minimal intervention we always startwith the most delicate techniques, soft brushes,going gradually if necessary and possibly withmore aggressive techniques such as surgicalscalpels, ultrasonic chisels and pins, pneumaticchisels, laser, microdrills, micro sandblasting,pressurizer water jets and by other means.

When calcareous deposits cannot be removedby mechanical means we are compelled to usechemical means. Cleaning with the use of che-mical compounds must be strictly controlled, andmild substances must be used that cannot da-

mage the physical and chemical structure of theobject.

Encrustations of calcium carbonate or calciumsulphate on ceramic material may be treatedwith EDTA disodium (acid) or tetrasodium(basic) salt. A solution of EDTA in deionised ordistilled water is a sequestering or chelatingagent: complexes are formed with some metallicions (Ca++, Mg++, Cu++ and Fe++) making the

encrustations soluble. The sequestering agent isused to remove insoluble salt deposits, concreti-ons and metal stains by converting the metalinto a soluble form that can be rinsed away(PRUNAS, 2012). A solution of tetrasodium ED-TA salt (pH 11.5) works best for removing calca-reous encrustations, which are more soluble in abasic environment (HAMILTON, 1999). It can beapplied by pads soaked in a 10 to 15% solutionof tetrasodium EDTA salt in distilled water, andthen mechanically removed. After the chemicalcleaning procedure the object must bethoroughly rinsed in distilled water to achieve aneutral pH level. For the same objective we canalso use ionic (cationic/anionic) exchange resins(AMBERLITE IR 120 H, AMBERLITE 4400 OH).We use them by mixing the resin in the form ofpowder with demineralized/distilled water andthen applying it using a wooden or plastic stick(it must not be of metal) on a layer of Japanesepaper, which protects the ceramic from directcontact with chemical compounds. Their advan-tage is that they do not penetrate into thematerial's porosity and so do not affect the arte-fact. This property is at the same time a disad-vantage when we need to remove gypsum orother salts from a material's deep porosity. They

Figure. 3. A ceramic figurine covered by calcareousdeposits and deposits of marine organisms (Photo: M.4urkovi5)

Figure 4. A ceramic amphora on which we see the tra-ces of an iron object that had rested against it in the formof iron oxides (Photo: M. 4urkovi5)


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do not have an effect on thick encrustations sin-ce they react only with the surface of the encrus-tation (PRUNAS, 2012).

Removing iron and copper oxides

Iron and copper oxide stains occur when anoxidised metal object is located near or in con-tact with a ceramic or stone object and metaloxide particles pass to the structure of the stoneor ceramic. Iron and copper oxides are formedby the degradation of metals caused by thecombined action of water and air, sometimesaided by atmospheric pollution. Oxides penetra-te deep into the pores of ceramic materials andcreate reddish - brown to black stains in the ca-se of iron oxide, and blue - green stains in thecase of copper oxides. We often find iron andcopper oxide stains on objects extracted fromthe sea. They can be cleaned with cotton pads,paper pulp pads or absorbent clays (Sepiolite)soaked with distilled water. A solution of disodi-um EDTA salt in distilled water is more effective,being the most efficient in removing iron andcopper oxide stains, as they are more soluble in

an acid environment. We use a 15 to 20% soluti-on in distilled water on ceramics to remove sta-ins, applied in the form of soaked cotton, paperpulp pads or absorbent clays (Sepiolite). Whenapplying soaked paper pulp or absorbent clays itis recommended that a layer of Japanese paperbe applied to the object followed by the pulp/clayto prevent the penetration of the material into

porosities. After the use of disodium EDTA saltwe need to liberally rinse the object in distilledwater to achieve a neutral pH level (pH 7).

Iron oxides can be removed from objects by su-bmerging them in a 10 to 25% solution ofhydrogen peroxide. The amount of time requiredto remove a stain varies from a few seconds toseveral hours. Rinsing is not required after theuse of hydrogen peroxide. We must be awarethat bubbles produced by the reaction ofhydrogen peroxide with the stains can detach

Figure 5. A ceramic jug with orange stains caused bythe infiltration of iron oxides (Photo: M. 4urkovi5)

Figure 6. Large Iznik plate covered with iron oxides before and after conservation - restoration tre atment (Photo: M.4urkovi5)


the glaze or damage the surface of the ceramicif it is not really well preserved and sound.

Removing organic deposits

Organic deposits are created during the decom-position of living organisms or by the sedimenta-tion of organic substances. Larger deposits areremoved mechanically, while infiltrated depositscan be removed by submerging the object in a10 to 25% solution of hydrogen peroxide. Smal-ler deposits can be removed by applying a padsoaked in a 10 to 25% solution of hydrogenperoxide over affected areas. Washing the ob-ject in a 5% solution of tensioactive hygieniccompound (C 2000) in distilled water with brus-hing is recommended for the removal of carbo-naceous, fat and oily substances and proteicmaterials. The object can be cleaned with a ten-sioactive concentrated preservative (New Des)based on quaternary ammonium salts, whichhas an effect on microorganisms and biologicalpatina. It is used as a solution of 5% preservati-ve in distilled water. It does not need rinsing intap water after the treatment.

Enzymes (amylase, lipase or a mix of enzymes)may be used on fats, carbohydrates and prote-ins to enable them to be washed away.

3. DESALINIZATION

We have already touched upon the problem ofsoluble salts and moisture in porous materials inprevious chapters, in this case affecting cera-mics and stone. Soluble salts are most oftenpresent in objects extracted from the sea, butwe also find them in objects that were found inthe open or underground in seaboard areas.They are removed by the desalination process.

Desalination is defined as the maximum possib-le reduction of the salt content of a material ef-fected through its extraction. Extraction is under-taken to achieve three principal objectives: mini-mise the deterioration of the material caused bythe process of crystallisation/dissolution of solu-ble salts, prevent future deterioration and avoidthe alteration of subsequent restoration proce-dures such as consolidation or integration(ZORNOZA - INDART, 2009, 2031-2042).

The desalination of an artefact from a marineenvironment is most efficiently carried out by

submerging the object in a bath of clean waterthat is periodically changed. Tap water is usedin the initial phases of desalination, followed bydistilled water in subsequent baths. It is impor-tant to proceed gradually in order to avoid theoverly rapid release of salts, which could causeadditional damage to the object. Theconductivity of the water is measured before andafter every change of water with a conductivitymeter and/or potentiometric titration as an indi-cator of the quantity of salts that have been sec-reted. When the quantity of salts (conductivity)has been reduced to a minimum constant valuethe process of desalination can be completed,i.e. the object can be taken out of the bath and

allowed to dry in a shaded location. Care shouldbe taken that the object is not exposed to signifi-cant oscillations in temperature during drying.

There are a number of methods of desalinationby soaking:

Desalination in closed baths with frequentchanges of water and measurements.

Desalination in baths with pumps that im-prove water circulation. This prevents the

Figure 7. The fracturing of ceramic caused by the presen-ce of soluble salts (Photo: M. 4urkovi5)


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occurrence of salty pockets in hard to rea-ch places under and inside the object andthereby facilitates and accelerates theprocess of salt secretion. Waterconductivity measuring is carried out atevery change of water.

Desalination in flowing water baths. Thisis the most effective, but also the mostexpensive procedure. The large quantitiesof tap and distilled water used presents aproblem. Conductivity measurements aremade during the entire process.

In the case of low - fired or extremely large ob-jects it may be prefer able to undertake desalina-tion using pac

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Conservation of Underwater Archaeological Finds Manual 2-Libre

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