A COMPARATIVE STUDY OF THE USE OF AQUAZOL IN PAINTINGS CONSERVATION
By Elisabetta Bosetti
AQUAZOL IN PAINTINGS CONSERVATION
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 e‐conser vation
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 . 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. 73
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.
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 74
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 e‐conser vation
AQUAZOL IN PAINTINGS CONSERVATION
Table I. Samples characteristics.
Type of Canvas
Thread Density (cm2)
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
Table II. Physical Properties of Aquazol .
White to pale yellow
Soluble in water and most polar solvents
Figure 5 (upper left). Backside of original painting. Preparation of 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 produce sample S4. Detail of the detachment obtained by heating and crumpling the sample.
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 76
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). e‐conser vation
AQUAZOL IN PAINTINGS CONSERVATION
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.
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.
AQ500 and AQ200 revealed an interesting fluo‐ rescence, with higher intensity in AQ200. PVA had no fluorescence.
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, e‐conser vation
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 77
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. e‐conser vation
AQUAZOL IN PAINTINGS CONSERVATION
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).
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/ e‐conser vation
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. 79
Diagram 1. Polymer drops on Kraft paper. Evaluation of the surface tension of drops.
Diagram 2. Deformation of the Kraft paper caused by polymer drops after drying process.
AQUAZOL IN PAINTINGS CONSERVATION
Diagram 3. Summary diagram of the results testing on canvas samples. The two molecular weights of Aquazol have been put together 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 after application (with brush) of AQ500 after drying (400x magni‐ fication). Figure 25 (bottom right). Canvas sample, Canvas A – linen after application of AQ500, after drying on the back side of the sample (400x magnification).
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.
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 of canvas sample, Canvas D – linen. Front (top) and back (below) of the sample.
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 e‐conser vation
AQUAZOL IN PAINTINGS CONSERVATION
Figures 29 and 30. Canvas sample, Canvas A â€“ linen with applied AQ500. The image shows a frame from the video recording at the 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) the application of AQ200 and after drying (20x magnification).
Table III. Samples generated from actual paintings.
Age of painting
Gesso + multiple grey oil layer
Matte acrylic medium + dye
Damage and needed treatment Tear + paint layer detachments (original damages) Consolidation + impregnation Paint layer detachments (artificially caused) Adhesion with heat treatment Cracks in paint layer + detachments (artificially caused) Impregnation + adhesion Paint layer detachment (artificially caused) Adhesion with heat treatment Tear (artificially caused) Mending/impregnation with heat treatment 83
Figures 33 and 34. Sample from actual painting (S2) tear and detachment of paint layer before the application of AQ200 and the flattening 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).
Table IV. Performance evaluation of Aquazol in situ.
Consolidation + impregnation
Distribution on threads and between particles of paint layer
Adhesion with heat treatment
Impregnation + adhesion
Adhesion with heat treatment
Tearâ€?mending with heat treatment
Flattening of paint layer with heated spatula maintaining adhesion properties Distribution between contact surfaces of paint layer flakes and cracks Flattening of paint layer with heated spatula maintaining adhesion properties Impregnation, adhesion and flattening of paint layer with heated spatula maintaining adhesion properties
Very satisfactory Very satisfactory Very satisfactory Great and very satisfactory eâ€?conser vation
AQUAZOL IN PAINTINGS CONSERVATION
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 of AQ200 (20x magnification).
behaviour of the polymers. However, it was posâ€? 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.
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. eâ€?conser vation
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 85
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
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.
Appendix At 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. Acknowledgements The 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.
References 1 The testing was not intended to be a complete treatment,
i.e. following completion of removal of residual polymer from the painted surface and the perfect juxtaposition of the flacks of colour.
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AQUAZOL IN PAINTINGS CONSERVATION
lidant”, in V. Dorge and F. Carey Howlett (ed.), Painted Wood: History and Conservation, The Getty Conservation Institute, Williamsburg, Virginia, 1994
 J. Arslanoglu, ”Using Aquazol: a brief sum‐ mary”, AIC Paintings Speciality Group Postprints, 32 Annual Meeting, Portland, Oregon (2004)
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ELISABETTA BOSETTI Conservator‐restorer Contact: email@example.com 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. 87
No. 24, Autumn 2012 ISSN: 1646‐9283 Registration Number
125248 Entidade Reguladora para a Comunicação Social
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