POL LUTE D RAI N AND M ONUME NT S

The pH of rainwater usually has a value of 5.5, allowing the life of flora and fauna without damaging resistant rocks like marble.

MARBLE

Thanks to the chemical and mechanical resistance to weathering, since ancient times marble was used to decorate prestigious buildings with capitels, columns or even statues and monuments.

However, the industrialization of the nineteenth century led to the increase of gas in the atmosphere, above all components as:

1.  Dioxide and sulfur trioxide (SO2 and SO3)

2.  Nitrogen dioxide (NO2)

3. Carbon dioxide (CO2)

T H E S E G A S E S R E A C T W I T H T H E H 2 O, G I V I N G T H E F O L L O W I N G A C I D S

1.SO2 + H2O ---> H2SO3 (sulphorous acid)

2.SO3 + H2O ---> H2SO4 (sulfuric acid)

3.2NO2 + H2O ---> HNO2 + HNO3 (Nitrous Acid and Nitric Acid)

4.CO2 + H2O ---> H2CO3 (carbonic acid)

These reactions can lower the pH value up to 2, resulting in a serious damage especially to the marble changing it from calcium carbonate (CaCO3) in gypsum (Calcium sulfate: CaSO4), more easily damaged by atmosphere agent.

Rainwater removes the gypsum that has been formed and so a new portion of the marble is exposed to the action of acid rain with a consequent progressive and continuous erosion of the building or of the artifact artistic.

The blackening

and air pollution

I TA LY H A S T H E G R E AT E S T C O N C E N T R AT I O N O F H I S T O R I C A L A N D A R T I S T I C H E R I TA G E O F T H E W H O L E W O R L D

In the national territory, over 60,000 areas of cultural interest have been registered in the risk map (icr 1996).

In recent decades there has been a rapid degradation due to pollution as the major cause.

The decay of a work of art begins immediately after its completion and the speed depends on the materials and external agents.

The speed of action is increased by the presence of carbonaceous particles to which are attributed also the blackening on stone surfaces of monument or historic building.

Air pollution affects especially the degradation of the artistic heritage as determines the change of the gases and causes harmful chemical reactions. Limiting greenhouse effects meets the protection of art.

The index of biological contamination takes into account the level of biological events on monuments.

THE ORGANISMS PRESENT ON THE WORKS OF ART CAN BE:

• Natural , i.e. lichens, mosses

1. These are deposited on the surface of monuments

2. Frost3. Salt Crystallisation4. Microclimate5. Thermal shock6. Chemical

• Anthropic ( caused by humans activities )

1. Pollution 2. Acid rains

We can infer the degree of microorganism colonization by sampling the sediments and calculating the amount of ATP (adenine-tri-phosphate).

In 1995 the Ministry for Cultural and Environmental Heritage promoted the Risk Map of Italian Cultural Heritage.

It still protects our territory and provides its members instruments for scientific and administrative support.

The risk map also allows us to calculate the risk of loss of all cultural heritage and to know their distribution on the Italian territory

The first ever comprehensive evaluation of the factors of degradation was made in Umbria which proved to be effective in the dramatic occasion of the earthquakes in Friuli.

THE MOST AGGRESSIVE SUBSTANCES FOR

MONUMENTS

CARBON DIOXIDE : it’s a natural component of the atmosphere.

In these years the concentration of CO2 has increased because of the fossil fuels adopted in the domestic heating and in industrial processes.

Calcareous stone artefacts and calcareous

Sandstones are dissolved by slightly acidulate water.

SULPHURE COMPOUNDS (SO X )

It’s principally present in the atmosphere as sulphur dioxide (SO2), hydrogen sulphide (H2S) and sulphates (SO4).

In combustion processes sulphure is oxidized into sulphur dioxide(SO2).

The presence of sulphure oxides in the atmosphere is the reason for the formation of gypsum.

The latter concerns stone material and bronze.

This process causes the loss of the superficial layer of the material.

OXIDES OF NITROGEN(NO X ) :

They are all the compounds between nitrogen and oxygen in the different oxidation states.

Generally nitrogen oxides are oxidized in the atmosphere by nitronic acid that corrodes the material surface.

ATMOSPHERIC PARTICULATE

They are carbon particles produced by the combustion of fossil fuels wich settle on stone artefacts, bronzes, paintings and frescoes damaging them.

ATMOSPHERIC PARTICULATE

All the kinds of particles can be found in the black crusts that cover monuments.

T H E PA RT I C U L AT E B E C O M E S A N I N T E G R A L PA RT O F T H E M AT E R I A L

T H AT F O R M S T H E M

The substances that can deteriorate a work of art may be released from different sources like:

-COMBUSTION PROCESSES: like carbon dioxide, sulphur dioxide and carbon particles;

-MEANS OF TRANSPORT: that produces carbon nitrogen and sulphur oxides and particulate;

-PROCESSING ARTEFACTS: that introduce in the atmosphere sulphuric anhydride , hydrochloric acid , nitrogen oxides and particulate

GOOD CONSERVTATION PRACTICES

The synergy of both physical and chemical factors determines the degradation of a work of art, which causes subsequent restoration and cleaning. The resulting cultural loss is difficult to estimate in monetary terms, because of the intrinsic value of many artistic artefacts. Restoration and consolidation practices are often neither decisive nor definitive and must be repeated at regular intervals.

GOOD CONSERVTATION PRACTICES

The key objectives to be achieved in the protection and conservation of works of art can be listed as follows:

Slowing down of the degradation and consequent reduction in the loss of the original material

Restitution and preservation of the aesthetic contents of the monument

I T I S E S T I M A T E D T H A T , O N A V E R A G E , T H E R E S T O R A T I O N O F A R C H I T E C T U R A L S U R F A C E S C O S T S F R O M 5 0 0 T O 7 5 0 € P E R

S Q U A R E M E T R E .

This cost must be added with

Security charges Design charges Charges for provisional

deeds

Therefore, we can consider that the cost of the restoration reaches 1,000 - 1,500 € per square metre of surface. For example in Rome, as a rule, the restoration of surfaces, is performed at regular intervals of 25-30 years, corresponding to the Jubilees

The management system of geographic information allows us to represent on the risk map the relationship between territorial municipalities and distribution of cultural heritage.

M I N I N G T O W N O F T U R I N A N D S U P E R I M P O S I T I O N O F C U L T U R A L B E L O N G I N G

M I N I N G T O W N O F N A P L E S A N D S U P E R I M P O S I T I O N O F C U LT U R A L

B E L O N G I N G

Scientific Experiment

To prove the truth of transformation of marble to gypsum, we

conducted an experiment in the school laboratory, by the reaction of hydrochloric acid and sulfuric acid on stones such as marble and travertine.

Scientific Experiment

Usually the sulfuric acids make these stones easy to damage but we did this experiment also with hydrochloric acid to accelerate this process.

To realize the experiment, we needed the following materials:

- A piece of marble; - A piece of travertine; - Hydrochloric acid; - Dropper; - Sulfuric acid.

Materials

Once positioned the piece of marble and travertine for the

experiment, we dropped some sulfuric acid on marble and travertine.

Step One

Marble Travertine

As soon as let the acid, it reacted making

bubbles.

Step One

Marble Travertine

We repeated the experiment substituting sulfuric acid with

hydrochloric acid to have a faster reaction although usually the surfaces are transformed by sulfuric acid.

Step Two

Marble Travertine

In fact, the reaction we obteined with the

hydrocloric acid, was more visible and immediate then the other.

Step Two

Marble Travertine

However, although hydrochloric acid had accelerating the

process, before the final result we had to wait a day to see that the surface on which the solution had been applied, had become gypsum.

Step Three

Thanks to this experiment we have seen how due to acid rain,

in the long run (because of the low concentration of sulfuric acid) the marble becomes gypsum and then more subject to degradation.

Conclusion