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A COMPARATIVE STUDYOF THE USE OF AQUAZOLIN PAINTINGS CONSERVATION

By Elisabetta Bosetti

Aquazol (Poly(2‐ethyl‐2‐oxazoline), PEOX) is a water‐soluble synthetic resin that has been used in

conservation for about a couple of decades for consolidation, adhesion and lamination on materials of

very different type such as glass, wood, paintings, enamel and paper. It has been of the utmost

importance to learn more about this product in a practical context, especially because its non‐toxicity and

versatility promise easy application without health risks. This article is an empirical study with the main

goal of exploring and learning, through testing, observation and documentation, the physical and optical

behaviour of the polymer in a practical context in comparison with two other water‐soluble polymers:

polyvinyl alcohol and acrylic‐acid‐ester‐copolymer. The study had the focus on water solution during and

after application on canvas samples, paper and painted layers on canvas made with traditional and non‐

traditional materials.

Introduction

The idea of this project has been developed in

recognition of a lack of knowledge on the practical

application of the innovative materials from the

chemical industry in conservation, particularly

in the field of paintings.

The tendency to choose and use products that

are not specifically developed for conservation

purposes is quite common in conservation prac‐

tice. The choice can partly be based on recommen‐

dations from conservation professionals, but also

on scientific studies, which predominantly and

typically focus on the properties of the products

and rarely on how they work in conservation

practice. It is hoped that this study will be a

useful contribution to a better knowledge on the

use of Aquazol.

Literature about this versatile polymer traces the

use of Aquazol in the field of conservation to the

early 90’s, mainly in the USA, but scientific studies

have focused on this synthetic resin since the 80’s

[1‐3]. Its use and application in conservation

treatments ranges widely. Initially, it was analysed

for conservation purpose as consolidant for glass.

Subsequently its use expanded from enamel to

lantern slides, as consolidant in paintings or

medium in gesso filling as an environmentally

compatible alternative to animal glue and testing

on remoistenable mending tissues [4, 5]. Aquazol

satisfies the expectation of compatibility with

other conservation materials, and reversibility

in conservation terms, which in many cases is

the most desirable quality in conservation

treatments [6].

A considerable number of publications on Aquazol

can be found in literature, but when compared

with other similar synthetics, Aquazol is still less

known. However, research done to date on Aquazol

shows interesting and satisfactory overall results

with a prevalence of advantages compared to its

disadvantages.

Due to its varied properties, Aquazol corresponds

in many ways to a desirable solution for consoli‐

dation, adhesion and lamination. It is relatively

stable at room temperature and pressure, its pH

is neutral when in aqueous solution, it is ther‐

mally stable and stable under artificial aging

conditions, it is compatible with a broad range of

materials, it is non‐toxic and its solutions are

very easy to prepare [7, 8]. This polymer also has

the property of being soluble in both water and

in the most common polar solvents used in

conservation.

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AQUAZOL IN PAINTINGS CONSERVATION

Materials and Methods

It was sought to undertake the study simulating

conditions where consolidation and adhesion

interventions were needed in order to observe

the polymers when in situ after treatment, but

also during the application. The reason of choos‐

ing this method was to achieve a better and more

concrete comprehension of the polymers’ proper‐

ties, and furthermore to have a visual statement

of fact of their behaviour when used in painting

structures. To operate in accordance with this, it

was necessary the use of samples from real

paintings. This way, it has been possible to

perform tests on naturally aged samples allowing

the study to come as close as possible to the

conditions of real conservation treatments.

The samples were produced using five paintings

of no historical value coming from flea markets,

antiquarian stock and from the author’s property

(Figures 1‐4). These different types of paintings

were chosen with the intention of having a relati‐

vely varied range of materials and stages of aging,

spanning from approximately 1 to 71 years old.

One of the oldest paintings had already structural

From left to right, up to down:Figure 1. Original painting used to produce sample S1.Figure 2. Original painting used to produce sample S2.Figure 3. Original painting used to produce sample S3 and S3a.Figure 4. Original painting used to produce sample S4.

ELISABETTA BOSETTI

74 e‐conservation

damages such as cracks, paint layer detachments

and losses. The other four paintings had no rele‐

vant damages.

To follow the purpose of the study, it was neces‐

sary to produce damages artificially. These were

made mechanically on three paintings by using a

pointed tool to achieve tears, detachment and

holes. The fourth painting, made with acrylic

colours, was still very flexible in its structure. To

achieve detachment of the paint layer, it was

necessary to use heat to make the paint layer

more brittle. A square piece of the painting was

cut and heated at around 80°C in an electric

oven for about 2 hours. Afterwards, the paint

layer detachment was obtained by crumpling

the painting piece (Figures 5‐8).

In addition to this, samples of canvases were

also used to perform testing to observe optical

and physical behaviour of the polymers. Specifi‐

cally, the samples were took from four different

types of linen canvas with different thickness

and on a sample from a single synthetic canvas

(polyester), as summarised in table I.

This study is based on a comparative method

between four polymers used in conservation. The

tests were carried out with Aquazol 200, Aquazol

500, and two other polymers in water solution/

dispersion: Mowiol, a polyvinyl alcohol (PVA) par‐

tially saponified, and Acronal 500D, an acrylic‐

acid‐ester‐copolymer. In the preliminary stage

of the study, tests on transparency and surface

tension were also performed with these four

polymers on kraft paper and polyester films

(Hostaphan).

There were many polymers that could have been

chosen to be compared with Aquazol. Among

many others, Mowiol and Acronal were chosen

due to the large experience the author has with

Sample Type of Canvas Thread Density (cm2)

A Linen 288

B Linen 195

C Linen 121

D Linen 182

E Polyester 255

Table I. Samples characteristics.

Physical State Solid

Appearance White to pale yellow

pH Neutral

Glass Temperature 69‐71°C

Decomposition temperature >300°C

Solubility Soluble in water and most polar solvents

Table II. Physical Properties of Aquazol [10].

AQUAZOL IN PAINTINGS CONSERVATION

75e‐conservation

these synthetics, of over 20 years, when a cold

application is desirable. Animal glues were not

included in this study because it was limited to

polymers used in conservation although both hide

and sturgeon glue were a natural choice due to

their similar properties to Aquazol when dissolved

in water.

Aquazol polymers are commercially available in

four different molecular weights: 5, 50, 200 and

500 g/mol. For this study, two of the four, Aquazol

200 and Aquazol 500, were chosen for two reasons.

First, these two molecular weights have already

been studied and widely tested [8, p. 109; 9].

Furthermore, they have been identified as most

satisfying and preferred than the two other

options by conservators who use Aquazol in their

treatments due to good quality in both applica‐

tion and preparation. Second, Aquazol 5 and 50

are more difficult to find. The physical properties

of Aquazol are listed in Table II.

In this article, the polymer names will be used in

abbreviated form for easier reference: Aquazol 200

(AQ200), Aquazol 500 (AQ500), polyvinyl alcohol

(PVA), and acrylic‐acid‐ester‐copolymer (AC).

Figure 5 (upper left). Backside of original painting. Preparationof sample S1.Figure 6 (lower left). Original painting used to produce S1.Detail of the back of the painting artificially made damages.Figure 7 (upper right). Preparation of samples S2 and S3.Figure 8 (lower right). Original painting used to producesample S4. Detail of the detachment obtained by heating andcrumpling the sample.

ELISABETTA BOSETTI

76 e‐conservation

Visual documentation was done with a digital

camera Canon Ixus 210 and USB powered micro‐

scope (20x‐400x magnification) Veho VMS‐004

Discovery Deluxe, taking snapshots and video

recordings of the drying process. Since ultraviolet

(UV) lamps are used by conservators to identify

recent interventions, the samples were observed

under UV radiation at 366 nm in order to assess

the fluorescence of the polymers.

Results and Discussion

Preliminary testing

The procedure was defined preliminarily, start‐

ing with simple observation of the polymers in

solid state with natural light and UV to determine

if there were differences in fluorescence between

the polymers (Figures 9 and 10). However, this

observation could not be done on AC because it

is not commercialized in a solid state but already

in water solution, although it was performed in

later treatments. The observation with natural

light revealed a yellowish appearance of AQ500

and AQ200, with major intensity for the latter.

The PVA does not have a colour and can be descri‐

bed as white slightly transparent. With UV light,

AQ500 and AQ200 revealed an interesting fluo‐

rescence, with higher intensity in AQ200. PVA had

no fluorescence.

Next, it was required to find the optimal polymer/

water ratio to be used in the tests. The optimal

concentration of the polymers in water solution

was determined by trying different percentages,

from 5% to 20%. The optimal concentration of

AQ500, AQ200 and PVA was found to be at 10%.

The criteria for the choice of this percentage for

all four polymers were based on the desire to

have the same parameter despite the recognition

that it would be possible to equally reach a similar

fluidity at different concentrations for each poly‐

mer. Although the fluidity of AQ200, AQ500 and

PVA was always quite similar even at different

concentrations, while AC, being already in liquid

form, at a lower concentration than 10% was

found to be too watery and weaker. In order to

achieve a similar fluidity as the other three

polymers, it would have been necessary to have a

very high concentration with the result of moving

the study too far from the reality of an actual use

of AC in a conservation treatment. The concen‐

tration at 10% was therefore also an acceptable

compromise for performing tests. The polymers

in question are readily soluble in water at normal

Figure 9. Aquazol 200‐500 and PVA in solid state with visible light. Figure 10. Aquazol 200‐500 and PVA in solid state with UV light.

AQUAZOL IN PAINTINGS CONSERVATION

77e‐conservation

room temperature, except for PVA that must be

heated to 80°C to achieve a complete solution.

In aqueous solution, the polymers have different

appearances both in consistency and in fluidity.

Concerning their appearance while in solution,

AQ500 and AQ200 maintained the yellowish shade

as when in solid state but had a smooth and satis‐

factory fluidity; PVA’s appearance had a greyish

shade but a less satisfactory fluidity compared to

AQ500 and AQ200. AC was completely non‐trans‐

parent and had a watery consistency and fluidity.

To better observe and understand the solutions’

fluidity, transparency and surface tension, tests

were made by applying a drop of each polymer on

Hostaphan polyester film and Kraft paper, respec‐

tively (Figures 11‐ 15). The test on polyester film

revealed an equal and satisfactory transparency

of the thin layers that the polymer drops made

after drying. With UV it was possible to observe a

total lack of fluorescence, which could lead to the

assumption that the solely film produced by these

polymers hardly can be traced if used on inert

and transparent material. With this test it was

furthermore possible to pay particular attention to

the difference between the drops’ surface (Figu‐

res 16‐19). The thin layer formed by the drops of

AQ500 and AQ200 had a sticky surface for several

days after the application on the polyester film,

which caused dust particles to stick to the surface.

Drying time was not measured, but it was asumed

that it was about 4 or 5 times slower than the two

other polymers.

Up to down:Figure 11. Drop of water on Kraft paper.Figure 12. Drop of AQ200 on Kraft paper.Figure 13. Drop of AQ500 on Kraft paper.Figure 14. Drop of PVA on Kraft paper.Figure 15. Drop of Acronal on Kraft paper.

ELISABETTA BOSETTI

78 e‐conservation

Water

AQ200

AQ500

PVA

Acronal

On the Kraft paper, after the water drop, it was

interesting to note, in addition to the deformations

of the paper surface, where and how the polymeric

materials were distributed on the contact surface

between the drops and the paper (Figures 20‐22).

The level of deformations of the Kraft paper caused

by the polymer and water drops is summarized in

diagrams 1 and 2, where the degree of deformation

was expressed in arbitrary units between 0 and 8.

Testing on Canvas Samples

The goal of the testing was to measure chromatic

changes, flexibility, migration through the fibres,

distribution of the polymers on treated surface/

material and the intensity of the fluorescence

with UV after the application of the polymers in

water solution (Diagram 3).

It was interesting to observe the behaviour of

the polymers on high hygroscopic materials like

linen fibres to better understand the optical and

physical changes of the tested samples and, fur‐

thermore, to document the polymers’ migration

through the canvas weaving (Figures 23‐28). This

was due to the fact that the observation in a

painted structure could be misleading because of

the different composition of materials with dif‐

ferent physical behaviour (hydrophilic/ hydro‐

phobic), not to forget the difficulty of controlling

the capillary factor between layers.

Figures 16‐19 (left to right). Dried drops of AQ200, AQ500, PVA and Acronal on polyester film.

Figures 20‐22 (left to right). Dried drops of AQ200, PVA and Acronal on Kraft paper (20x magnification).

AQUAZOL IN PAINTINGS CONSERVATION

Aquazol 200 Aquazol 500 PVA ACRONAL

79e‐conservation

Diagram 2. Deformation of the Kraft paper caused by polymer drops after drying process.

Diagram 1. Polymer drops on Kraft paper. Evaluation of the surface tension of drops.

ELISABETTA BOSETTI

80 e‐conservation

Diagram 3. Summary diagram of the results testing on canvas samples. The two molecular weights of Aquazol have been puttogether in this diagram due to their very similar behaviour.

Figure 23 (left). Canvas sample, canvas A ‐ linen not treated(400x magnification).

Figure 24 (bottom left). Canvas sample, Canvas A – linen afterapplication (with brush) of AQ500 after drying (400x magni‐fication).

Figure 25 (bottom right). Canvas sample, Canvas A – linenafter application of AQ500, after drying on the back side ofthe sample (400x magnification).

AQUAZOL IN PAINTINGS CONSERVATION

81e‐conservation

Since the linen canvas samples had four different

thread densities, thickness and fineness, it was

possible to have a small range of results on which

to make some considerations from the optical

point of view. For example, chromatic changes of

the canvas samples with lower thread density

and fineness, after application and drying of

the polymers, were greater than those of the

canvas samples with higher thread density and

fineness. The temperature and relative humidity

during the testing were 23°C and 50%, respec‐

tively.

For the tests on the polyester canvas sample, it

was sufficient to choose only one kind of thread

density and fineness. Due to the hydrophobic

properties of these synthetic canvases, it was not

necessary to have a different type of spinning

and weaving because they would behave in the

same way and the results of the tests would not

give any interesting values to be compared with.

The particularity of the tests on synthetic canvas

was the minimal chromatic changes of the area

treated with the polymers observed with visible

light, whereas with UV light the polymers’ fluores‐

cence is higher than in tests done on linen canvas.

This observation imposes a particular attention

to the fact that the intensity of fluorescence of

the polymeric material is obviously closely related

to the type of material on which it is applied.

Therefore, the sole observation of the polymer

fluorescence is not determinant since its inten‐

sity changes considerably depending on the

physical properties of the materials on which the

polymer is applied. Furthermore, the observation

on the flexibility gives a low degree of stiffness

of the synthetic canvas.

The observation of the video recordings taken

with the microscope during the drying process

did not reveal any particular differences in the

From up to down:Figure 26. Testing migration of polymers through fibres.Application on different kinds of canvas samples.Figures 27 and 28. Testing migration and hygroscopicity ofcanvas sample, Canvas D – linen. Front (top) and back (below)of the sample.

ELISABETTA BOSETTI

82 e‐conservation

Figures 29 and 30. Canvas sample, Canvas A – linen with applied AQ500. The image shows a frame from the video recording atthe beginning (left) and end (right) of the drying process (400x magnification).

Figures 31 and 32. Sample from actual painting (S1) tear before (left) the application of AQ200 and after (right) theapplication of AQ200 and after drying (20x magnification).

Sample Age ofpainting

Canvas Ground Paint layer Damage and needed treatment

Tear + paint layer detachments(original damages)

Consolidation + impregnationPaint layer detachments

(artificially caused)Adhesion with heat treatment

Cracks in paint layer + detachments(artificially caused)

Impregnation + adhesionPaint layer detachment

(artificially caused)Adhesion with heat treatment

Tear (artificially caused)Mending/impregnation with heat

treatment

S1 67 years Linen Gesso Oilcolour

S2 ~40 years Polyester Gesso Oilcolour

S3S3a

71 years LinenGesso +

multiplegrey oil layer

Oilcolour

S4 8 years Polyester No Acryliccolour

S5 ~1 year Polyester NoMatte acrylic

medium+ dye

Table III. Samples generated from actual paintings.

AQUAZOL IN PAINTINGS CONSERVATION

83e‐conservation

Sample Treatment Expected results Performance evaluation

S1 Consolidation+ impregnation

Distribution on threads andbetween particles of paint layer

Great

S2 Adhesion with heattreatment

Flattening of paint layer withheated spatula maintaining

adhesion propertiesVery satisfactory

S3S3a

Impregnation+ adhesion

Distribution between contact surfaces ofpaint layer flakes and cracks Very satisfactory

S4Adhesion withheat treatment

Flattening of paint layer withheated spatula maintaining

adhesion propertiesVery satisfactory

S5Tear‐mending with

heat treatment

Impregnation, adhesion and flatteningof paint layer with heated spatulamaintaining adhesion properties

Great and verysatisfactory

Table IV. Performance evaluation of Aquazol in situ.

Figures 33 and 34. Sample from actual painting (S2) tear and detachment of paint layer before the application of AQ200 and theflattening with heat treatment (left), and after the application of AQ200 and after the flattening with heat treatment (right)(20x magnification).

Figures 35 and 36. Sample from actual painting (S3a) cracks in paint layer before (left) and after (right) the application of AQ200(400x magnification).

ELISABETTA BOSETTI

84 e‐conservation

behaviour of the polymers. However, it was pos‐

sible to note how they were distributed between

the fibres after the evaporation of water (Figures

29 and 30).

Tests on Painted Structures

The five different types of painting on canvas

samples were used to perform the tests with

Aquazol. The different painted structures are

summarised in Table III.

The testing on these samples from paintings on

canvas was limited to the observation of AQ200

and AQ500 in situ, particularly its ability to be

distributed between the layers in function to work

Figures 37 and 38. Sample from actual painting (S3) paint flack before (left) and after (right) adhesion with application of AQ200(20x magnification).

Figures 39 and 40. Sample from actual painting (S4) paint layer detachment before (left) and after (right) adhesion by application ofAQ200 (20x magnification).

Figures 41 and 42. Sample from actual painting (S5) tear before(left) application of AQ200 for mending treatment and after(right) application of AQ200 and mending treatment.

AQUAZOL IN PAINTINGS CONSERVATION

85e‐conservation

in adhesion, impregnation and consolidation

treatments1.

The polymer was applied on all samples in the same

way with a small brush helping it to penetrate

into the underlying layers by pushing the poly‐

mer into the cavities with small strokes.

All treatments had a satisfactory outcome. The

results are summarised in Table IV. The consolida‐

tion and impregnation treatment on S1 revealed

that the polymer was distributed in a great way

on the threads and between the particles of the

paint layer. On S2 and S4, where adhesion with

heat treatment was needed, the polymer allowed

to perform the treatment and flattening of the

paint layer with heated spatula at 45‐50 °C main‐

taining satisfactory adhesion properties. On sample

S3 the polymer was perfectly lying between the

contact surfaces of the paint layer flakes that had

to regain the adhesion and on sample S3a the

polymer penetrated smoothly into the paint layer

crack and filling satisfactory the gap. In the tear

mending performance on sample S5, where heat

treatment was needed, the polymer allowed to

perform impregnation, adhesion and flattening

of the paint layer with heated spatula at 45‐50° C

maintaining satisfactory adhesion properties.

Furthermore, the polymer did not change the

appearance of the matte paint layer (Figures 31‐42).

Conclusion

The outcome of this study confirms the high ex‐

pectations of an alternative non‐toxic product in

aqueous solution. Aquazol is the most versatile

1 The testing was not intended to be a complete treatment,i.e. following completion of removal of residual polymerfrom the painted surface and the perfect juxtaposition ofthe flacks of colour.

in application and demonstrate a minimal inter‐

action with the constituent materials of the pain‐

tings. These properties are of great advantage espe‐

cially in adhesion or impregnation treatments in

which it is highly desirable to control the polymer in

the substrates of painted surfaces. However, it is

important to note the tendency of this polymer to

impose both stiffness and chromatic changes (dark‐

ening) to the materials if they are hygroscopic.

Therefore, in a treatment that may include the

impregnation of a large area of a painted structure,

it may be necessary to assess the risk of having

significant chromatic changes that may have

subsequent unwanted effects.

AppendixAt the author’s current working place, she was

able to apply Aquazol on a wide range of materials

of museum objects and in different treatments

such as stabilization of lacquered and painted

wood and consolidation of highly hygroscopic

materials (hemp and clay). In the case where

materials were strongly hygroscopic and it was

not desirable to have a reaction with water, Aquazol

was dissolved in Acetone. Aquazol allowed the

execution of several treatments showing good

properties of compatibility with the different

materials in all cases.

AcknowledgementsThe author would like to thank The Danish Art

Workshops in Copenhagen (Statens Værksteder for

Kunst) for having granted the use of its conserva‐

tion premises where the study took place, and to

Mrs. Michela Dell’Anno for proofreading the text.

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ELISABETTA BOSETTI

86 e‐conservation

lidant”, in V. Dorge and F. Carey Howlett (ed.),

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ELISABETTA BOSETTIConservator‐restorer

Contact: info@elisabettabosetti.dk

Elisabetta Bosetti was educated as restorer at

Scuola per la Valorizzazione dei Beni Culturali in

Botticino, Italy in 1990. Since 1991 she has been

working in Denmark at major and minor museum

institutions operating on important national monu‐

ments and objects of art from the Danish Cultural

Heritage. She is currently restorer at The Danish

National Museum of Military History (Statens Fors‐

varshistoriske Museum) specifically at the project

for the installation of the new basic exhibition.

AQUAZOL IN PAINTINGS CONSERVATION

87e‐conservation

No. 24, Autumn 2012

ISSN: 1646‐9283

Registration Number125248

Entidade Reguladorapara a Comunicação Social

Propertye‐conservationline, Rui Bordalo

PeriodicityBiannual

CoverBackside of an Easel Painting

during the preparation of a sampleBy Elisabetta Bosetti

Editorial BoardRui Bordalo, Anca Nicolaescu

CollaboratorsAna BidarraDaniel Cull

Rose Cull

Graphic Design and PhotographyAnca Poiata, Radu Matase

ExecutionRui Bordalo

AddressRua de Santa Catarina, nº 467, 4D

4480‐779 Vila do Conde, Portugal

www.e‐conservationline.com

All correspondence to:general@e‐conservationline.com

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