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Aspects of Longevity of Oil and Acrylic Artist Paints

Professor Frank N. Jones
Coatings Research Institute
Eastern Michigan University

This article will compare acrylic and oil artist paints from the point of view of a scientist who specializes in coatings. It is not meant to be the “end-all” source on the topic. However, it is meant to make the reader more informed regarding long-term durability issues for both these materials.

Below are three excerpts from recent artists’ list serves and internet chat rooms regarding the quality of oils and acrylics and the information available to them. These statements will help guide us as we explore the archival qualities of oil and acrylic artist paints.

- “Acrylic paint is the MOST stable and permanent material available to the artist today and if properly used will outlast all other materials.” [1]

- “One should beware of acrylic paints…At first…they were thought to be wonder media, but the binder has aged faster than oil colors and has caused the colors to yellow.” [2]

- “Man o man…so much information and it’s all good.” [3]

The first two people making the statements above feel strongly in their differing opinions, so where does that leave the artist? Probably uncertain about long-term durability of the materials they use. This article will help the artist become more aware of the issues associated with each material by focusing on such areas as film formation, film degradation, cracking, yellowing, cleanability, adhesion, and fading. This will give them the knowledge necessary to make an informed decision about the medium they use and what their artwork might look like in 500 years. In order to do this, we must first understand how paint films form.

1. Film Formation

To visualize the polymer molecules that hold paint films together, imagine a large mass of cooked spaghetti, with very long, strong strands. The strands are roughly analogous to polymer chains. The mass of material can be deformed because individual strands can bend and slide past one another, but movement is partly restricted by tangles. Touching this mass, one would sense that it is solid but not rigid; it is rubbery. Now imagine that we begin randomly gluing strands together at small points where they intersect. These connections furnish additional resistance to deformation. As we glue more and more strands together, the mass becomes more and more rigid. Finally, when the strands are all glued together at many points, the mass becomes very rigid and can be deformed only by breaking strands. The mass resists deformation, but under sufficient stress, will crack. The gluing together of individual strands is analogous (again roughly) to what polymer chemists call “cross-linking.”

On the canvas, acrylics and oils end up as high molecular weight polymer (see Glossary) films, essentially thin layers of plastic, usually containing a lot of pigment particles. But there are big
differences as to how they get there.

  • Oil paints in the tube are primarily vegetable oils, such as linseed oil, and pigment. Oils harden after they are applied to the canvas in a complex chemical process in which they react with oxygen. This process forms longer chains and many cross-links, leading to a cross-linked network of polymer. Because the oil molecules were relatively small at the start, many cross-links are required to reach a satisfactory state of hardness. The chemical reactions get slower as the film hardens, but they never completely stop (under normal display and storage conditions). Over time, continuing cross-linking can cause the film to become too brittle.
  • Acrylics are polymerized before the paint is manufactured, and no further chemical reactions are needed to form a film. The acrylic polymers are very large molecules (long strands) that form films through a process called coalescence (see Glossary) and do not need to be cross-linked to form a good film, although sometimes they are polymerized in a way that induces a small level of cross-linking. Recently painted acrylic films are softer, more flexible and less brittle than oil paint films (except perhaps at cold temperatures – see below). Acrylic films can undergo chemical changes as they age, but when a painting is kept indoors these changes that cause hardening, are very slow.

Now that we have a better understanding of how films form, we need to explore the causes of film degradation.

2. What can cause paint films to physically degrade?

Polymer films can undergo degradation in several ways. Two common ways can be classified as (1) chemical changes that increase cross-linking beyond the optimum level and (2) chemical changes that gradually break the polymer chains. Excessive cross-linking makes paint films brittle and vulnerable to cracking and flaking. Breakage of polymer chains results in smaller molecules, and if a large number of chains is broken, the films weaken and in extreme cases, disintegrate.

As noted above, oils would not harden without cross-linking, which for artist oils, usually takes months to reach an optimum level. By then, the chemical changes that cause cross-linking will have slowed, but they do not stop. The ongoing chemical changes cause oils to become harder, less flexible, and more brittle as they age.

There are also chemical reactions that can break the polymer chains in oils. The most common is chemical reaction with water. This reaction is usually slow, but it gets much faster if the paint film is exposed to humid air under alkaline conditions. This becomes a problem if the paint is formulated with alkaline pigments or if it is applied over an alkaline surface. Alkaline pigments may cause general deterioration, and alkaline surfaces may cause loss of adhesion. Masonry (brick, concrete, plaster, grout, stucco) surfaces are often alkaline, and it is undesirable to paint them with oils.

On the other hand, acrylics do not need to cross-link to form good films. The acrylic polymers used in modern acrylic paints are designed with the goal of making them resistant to chemical changes resulting from reactions with oxygen and water and by exposure to ultraviolet light. This goal is not completely achieved, and chemical changes occur slowly as paintings age. The changes are slow outdoors and much slower especially under indoor conditions. While it is not known how long acrylic films will retain their physical qualities, evidence presented below suggests they will last hundreds if not thousands of years. The chemical changes that could occur might either cause chain breakage or additional cross-linking. Lastly, the combination of humid air and alkaline conditions has little effect on acrylics, making them a paint of choice for alkaline surfaces such as masonry and plaster.

Pigments can influence degradation rates in several ways. First, the pigment particles themselves may deteriorate, usually causing a change in color. Fading is discussed below in Section 7. Second, pigments may affect the polymeric binder. For example, certain grades of titanium dioxide white pigments can catalyze photochemical deterioration; in the most appropriate grades of titanium dioxide, each particle is coated with glass and/or alumina to prevent this. As another example, high loadings of many types if pigments can make the paint harder and less flexible; this is generally a manageable problem, but high loadings in paints that tend to embrittle with age could potentially accelerate problems such as cracking. On the other hand, certain pigments such as iron oxides and carbon blacks are good UV screeners and generally enhance the outdoor weatherability of paints.

3. Cracking

Above is an example of an oil painting circa 1950 (artist unknown)
becoming brittle and cracking over time.

What are the consequences of these different chemistries? Oil paints become somewhat brittle as they cure, and the ongoing chemical changes will gradually increase this brittleness as they age. As a result, oil paints are increasingly vulnerable to cracking over time. Mayer’s compendium on artist materials [4] lists seven expedients that will minimize the tendency to cracking, including proper preparation of substrates, painting fat over lean and avoiding painting fast drying colors (e.g. burnt umber) over slow drying colors (e.g. alizarin crimson). Nonetheless, the author has observed that many, if not most, 100+ year-old oil paintings in several leading museums have cracked, as have some relatively recent paintings. Thick films on flexible grounds, such as canvas, appear especially vulnerable.

At normal indoor temperatures, acrylic paintings are much more flexible than oils. Thus, newly painted acrylics are expected to resist cracking better than newly painted oils in these conditions, even in very thick films. At low temperatures, however, the acrylics become brittle. Typically their flexibility drops sharply at temperatures a bit above freezing, say between 0 and 15 oC (32 to 59 oF), depending on the color, the composition of the acrylic, and the relative humidity. [5] Oils also become more brittle when cold, but embrittlement occurs at temperatures below freezing. Mecklenburg et.al. have shown that significant drops in temperature from 23o C down to below freezing at very low humidity can create stresses in a fairly young 13 year old oil paint film that will exceed its breaking point. [6] Both types of paintings should be handled very carefully when they are cold, especially when the air is dry. [7]

Do artists still work in freezing garrets? If so, oils will work better. The temperature at which the paint is applied is more of a concern with acrylics than with oils. Acrylic house paints should not be used when the temperature is below about 5 oC (about 40 oF) or when the temperature is expected to fall below this level for 4 to 8 hours after the paint was applied. The reason is that strong, coherent films cannot form at low temperatures, and even if the film later becomes warm, it will never recover. Acrylic artist paints are similar. To be on the safe side, they should be used only at temperatures above 10 oC (about 50 oF), and the painting should be kept above this temperature for several days after it has dried. [8] Acrylics painted and dried under cold conditions may look OK, but the films will be less durable and more vulnerable to cracking. Oils, on the other hand can be used at freezing temperatures or below.

While newly painted acrylics will be more crack resistant than newly painted oils, the question is how the film properties change with age. We know a lot about acrylic films for other applications (briefly described in Section 9) but only a few published studies concern artist paints. In one series of studies, Prof. Whitmore and Dr. Colaluca at Carnegie Mellon University attempted to accelerate the deterioration of “Liquitex Acrylic Gloss Medium” films. [9,10] “While films of Liquitex gloss medium did photo-oxidize upon exposure to ultraviolet light, the material generally demonstrated the remarkable photochemical stability associated with this class of acrylic polymers. In comparison to the mechanical property loss under UV-B exposure, tensile strength loss under UV-A lamps would have been observed only after about 200 days, a dose of near ultraviolet light equivalent to about 5,000 ‘museum years.’” [8,9] Encouraging as this conclusion is, one must recognize that accelerated testing of paints is notoriously unreliable, especially when the acceleration factor is high. In this study the factor was about 8700:1 – one museum year = about one hour of accelerated testing. Furthermore, many paintings are subjected to rough handling and exposed to light, humidity, and temperature fluctuations more severe than they would encounter in a museum.

Shown above is a Fluid Acrylic Naphthol Red Light film forming at ambient temperatures (left), at temperatures 38° - 40° F (center) and at 26° - 28° F (right). This clearly demonstrates acrylics' inability to form coherent films below 49° F.

 
Oils that have cracked are vulnerable to other problems. If adhesion is less than excellent, flakes of cracked films may delaminate. Even if the film remains attached to the ground, the cracks may open up, making them highly visible. Cracked oils may also suffer cupping, defined by Mayer as “concavities or depressions that sometimes exist inside the boundaries of a network of cracks.” [11]

4. Yellowing

Oils tend to be slightly yellow from the beginning, and the oxidation processes that cause hardening also cause additional yellowing. Different oils yellow to different degrees. Exposure to certain common chemicals, such as ammonia vapor from household cleaners, can make yellowing worse. There have been many efforts, spanning at least a century, to solve the yellowing problem. None have been completely successful. A detailed study of the chemical causes of yellowing by Professors Mallegol, Lemaire and Gardette at University Blaise Pascal in France concluded “Yellowing must therefore be considered as an unavoidable characteristic of drying oils and this must be kept in mind by users.”[12]

There is divided testimony in the literature as to how badly oils yellow. Crook and Lerner [13] state that “Linseed oil … has been used most widely due to its relatively rapid drying time. However, this is unfortunately accompanied by a tendency to yellow with age. Other, less yellowing oils have sometimes been used, especially for white paints and other light colors.”

On the other hand, many artists agree with Mayer when he [14] says that yellowing “…concerns only clear oil films and the use of oils in techniques other than normal oil painting” and that “correctly executed oil paintings do not turn yellow.” Perhaps the difference of opinion results from differing views as to how much yellowing is tolerable. This author’s observations in museums suggest that yellowing is discernable in whites and pastel colors of older oil paintings, although it is hard to tell how much of the problem is the paint and how much is the varnish. Franz Hals’ lacework may look white, but not when it is compared to a piece of white paper. The behavior of oil household paints suggests that the problem is significant. The whites gradually turned yellow and then tan when used indoors. This is one of the main reasons such paints have become almost obsolete in architectural applications.

The acrylic polymers used in high quality artist paints are almost colorless when they are first used, and with age they yellow very slowly under normal conditions. The very low tendency to yellow is the main reason acrylics are candidates for use as varnishes. Whitmore and Colaluca [15] reported slight yellowing of the acrylic medium they studied. Levison saw “no perceptible yellowness in any of the acrylic specimens [16].” Based on well established behavior of architectural and artist paints, it is safe to say yellowing of acrylics is much less of a problem than it is with oils.

5. Dirt pick up and cleanability

Oils have a clear advantage to acrylics regarding dirt pickup. Cleanability of oils is much more complicated, however [17]. Acrylic paint films are slightly porous and are softer than oil paint films, making dirt more likely to stick to them. Polymer molecules in the acrylics are at most only slightly cross-linked, making the films hard to clean because solvents and cleaners can degrade the acrylic surface. In theory, this problem could be overcome by increasing the cross-linking level in acrylics. Researchers have found practical ways to cross-link acrylics for other applications, e.g. varnishes for wood cabinets. Introduction of such technology into artist paints is possible but would require great caution because of the possibility of undesired effects on other properties and the uncertain effect on long-term durability. Research is also underway to define the best methods of cleaning unvarnished acrylics. (See article on Page 11 regarding the Samuel Golden Fellowship for Research into Modern Painting Materials at the National Gallery of Art in Washington, D.C.) The tendency to pick up dirt can also be reduced by varnishing acrylic paintings, but many painters prefer the appearance of the unvarnished surface.


Above is an example of a dirty acrylic film showing two types of cleaning methods. Pictured left to right is the dirty acrylic film, the dry cleaning method and a wet cleaning method.

6. Will the nose fall off?

Another aspect of durability is adhesion of the paint to its substrate. As Mayer points out, “linseed oil is not a strong adhesive” and the same could be said of the acrylic binders used in artist paints. What is most important is that with proper use both oils and acrylics are capable of giving fully satisfactory adhesion, and with improper use they are likely to fail. As with most paints, the most critical factor in obtaining good adhesion is to properly prepare the substrate (“the ground”). Gottsegen extensively discussed grounds for oil painting. [18] With oils, canvases must be undercoated with a ground that can protect the canvas from the oil. With acrylics, undercoating is desirable but not essential. Artists use many substrates, and recommendations for how to prepare them are published.

Overpainting artist oils with artist acrylics is definitely bad practice. The surface of hardened oil paint does not have “tooth.” It is too hard and often too shiny to afford good adhesion by acrylics. Paints stick better to rough surfaces than to smooth ones if other factors are equal. The roughness may be visible to the naked eye or microscopic. Either way, roughness increases the surface area upon which the attractive forces of the paint to the ground can act. On very rough surfaces, the paint may penetrate into recesses; then when it hardens mechanical interlocking, analogous to dovetail joints, can strongly enhance adhesion. Thus, rough surfaces are said to have “tooth.” Primers usually have low gloss, evidence of microscopic tooth. Most acrylics have more tooth than most oils, and overpainting acrylics with oils has a better chance to work, but the artist should be aware of potential problems.

7. Will colors fade?

Fading has been a problem for centuries. The stability of colors in both acrylic and oil paints depends primarily on the lightfastness of the pigments used. Most pigments used in contemporary artist paints are selected from lists of about 115 pigments that are established by ASTM International (formerly The American Society of Testing Materials) to be lightfast in acrylics [19a] and in oils [19b]. The lists are somewhat different to avoid alkaline pigments in oils and pigments that could be affected by water in acrylics. Artist paints are labeled with the lightfastness grade of the pigment; only pigments graded I (excellent) or II (very good) are considered suitable for archival paints. Certain special colors, such as fluorescent colors, are not lightfast. Use of lightfast pigments makes severe pigment-related color changes very unlikely for paintings that are kept indoors. Artists should be aware, however, that certain special colors, such as fluorescent colors, are not lightfast.


The GOLDEN Lab conducts exposure testing to be able to evaluate new materials for durability. This photo shows the test fence at Golden Artist Colors, Inc.

8. What can we learn from other types of paints?

Most (not all) artwork is kept indoors where it is protected from most of the damaging UV light in sunlight and from weather extremes. Window glass filters out the most destructive UV light in sunlight. It is widely accepted in the paint industry that indoor exposure is much less damaging to paint than outdoor exposure. In addition, it is widely assumed that paint that is durable outdoors will be very long-lived indoors.

The binders of exterior house paints evolved from vegetable oils to alkyd resins (starting in the 1930s) to acrylics (starting in the 1950s). It is almost universally recognized that each step was a major advance in outdoor durability. The acrylics used in contemporary artist paints are chemically similar to those used in high-quality house paint. Oil and alkyd paints (alkyds are synthesized from oils) are more vulnerable than high quality acrylics to the enemies of paint — ultraviolet radiation, water and heat. A tour of older neighborhoods will show examples of house paints that are severely cracked. These are almost always oil or alkyd paints that have become so brittle that they cannot accommodate expansion and contraction caused by temperature fluctuations and moisture. In contrast, acrylic house paints retain their flexibility for many years. By now, over 80 % of exterior paints used in the U.S. are water-borne “acrylics.” In this context “acrylics” means polymers that contain some acrylic monomer, but some also contain less expensive monomers such as styrene and vinyl acetate; the highest quality paints are 100 % acrylic. Better durability is a major reason for acrylics’ their popularity, but not the only reason. Soap and water clean-up and reduced organic solvent evaporating into the environment are also important advantages of acrylics. The alkyds that are still used as exterior house paints are used mainly as primers (where they are not exposed to direct sunlight) and by contractors who like the superior one-coat hiding of alkyds or who want to paint at temperatures near or below freezing (see section 2).

Most paints for home interior walls are based on poly (vinyl acetate) (“PVAC”). PVAC is used indoors because it is less expensive than acrylics, but it lacks satisfactory durability outdoors. PVAC based paints have been used by artists since the 1930s, but their usage appears to have been rather limited. [20] PVAC paints are used in art restoration and conservation. According to Horie, [21] attempts to remove them are sometimes quite successful and sometimes not. As media for archival painting they are almost certainly inferior to acrylics.

Automotive paints evolved from oils to nitrocellulose lacquers to alkyds to acrylics. Again, each step improved durability. The days are long past when cars had to be waxed and polished frequently to keep their shine. Introduction of acrylics made durable metallic car paints and durable clearcoats possible. Modern acrylic car paints are expected to retain good appearance for 10 years or more, even when the cars are driven and parked outdoors in harsh environments such as south Florida or Arizona. Acrylic car paints and acrylic artist paints both depend on the acrylic backbone for their durability. [22]

9. Are all acrylics the same, and are they really acrylics?

Learner at the Tate Gallery in London used sophisticated instruments to analyze synthetic paint binders used in 20th Century artist paints. [23] He studied paints on a large number of modern paintings, including paintings by many well-known artists. Learner found 100 % acrylic co-polymers on some paintings. He also found acrylic/styrene co-polymers, acrylic/ (vinyl acetate) co-polymers, poly (vinyl acetate), and vinyl acetate/vinyl neodecanoate co-polymers. Any of these latter types could easily be mistaken by artists for 100 % acrylics, since they are all based on emulsion polymers of similar physical appearance. Among the paints that were 100% acrylics, Learner found two types of co-polymers: [p(EA/MMA)] and [p(nBA/MMA)] (see Glossary).
The author has studied and researched a wide variety of paints for 35 years, and has recently researched artist paints [24]. Based on this experience he has developed opinions about what types of chemistry are most likely to perform well as archival artist paints:

  • Learner identified many kinds of polymers that have been used in artist paints. Two kinds, 100 % Acrylics and certain polyurethanes, are expected to be the most durable. Based on their performance in architectural paints, 100 % acrylics are preferable to acrylic/(vinyl acetates), acrylic/styrenes, and, especially, poly(vinyl acetates).
  • Unfortunately, in the commercial paint industry it has been common to represent acrylic/styrenes and acrylic/(vinyl acetates) as “acrylics.” It is not known to the author whether this practice spread to the artist paint field.
  • Among 100 % acrylics, [p(nBA/MMA)] is expected to be superior to [p(EA/MMA)]. Experience with house paints has shown that [p(nBA/MMA)] based paints weather better than [p(EA/MMA)] paints.

Quoting Learner’s paper [23]:
“Although both types of pure acrylic emulsion are utilized in current (artist) paint formulations, over the years there has been a gradual increase in use of p(nBA/MMA), as the production of many p(EA/MMA) emulsions has been terminated. This is because the principal commercial use of these emulsions, namely exterior house paints, requires a hydrophobic material and in general the [p(nBA/MMA)] copolymers show a superior hydrophobicity. Out of 10 brands of acrylic emulsion paint obtained in 1993, [p(nBA/MMA)] was found to be the binder in four of them, and most new formulations produced since then have been based on this emulsion.”

Combining the author’s opinions (unproven) with Learner’s findings (established facts), we can conclude that:

  • Many types of emulsion polymers and co-polymers have been used in artist paints.
  • In the early decades of “acrylic” paint use, it is likely that many artists used “acrylics” that were inferior to modern acrylics and were, perhaps, not acrylics at all.
  • The acrylics available today from reputable suppliers are probably better from the standpoint of longevity than some of those in use 25-50 years ago.
  • Information available today indicates that artist paints made with [p(nBA/MMA)] co-polymers are very likely to afford long-lived paintings.

10. What does practical experience tell us?

The most reliable way to assess the durability of paints is to evaluate them in actual service in the field. That is why car manufacturers send out survey teams to inspect cars that have been in use. They can observe cars in the field for their entire lifetimes, and they can tell from the Vehicle Identification Number (VIN) of the car exactly what day the car was painted and what paint was used. Artist paint manufacturers are not so lucky. Often, it is not known what brands of paint, ground, and canvas were used in a painting made twenty or fifty years ago, although their chemical types can be established by chemical analysis.

So, what do we know about artist acrylics in service? Most important, the vast majority of acrylic paintings made since the introduction of acrylics are holding up well, including many that were made with paints that were probably inferior to the acrylics available today, as explained in Section 9. Acrylics can crack, especially if they are roughly handled when they are cold [25].

Despite the good record of acrylics so far, some artists and conservators remain concerned about the long-term durability of acrylics because of their relatively short history. After all, acrylics have been used only for about 70 years and paints based on acrylic dispersions for about 50 years, while oils have been around for 500 years.

Such concerns have been fueled by a few well-publicized [26-29] failures of “acrylic” paintings by major artists. The failures of acrylics reported in the popular press have been variously described as fading, flaking, cracking, and crumbling. Beyond that, there is little information available that would enable a rigorous judgment of the causes of failure. One can only speculate based on knowledge and experience:

  • The most likely cause of fading is use of pigments that are not lightfast; this statement applies equally to oils and acrylics.
  • The most likely cause of flaking (presumably loss of adhesion) is painting over dirty or improperly prepared surfaces. Many other causes are possible, including poorly formulated paint.
  • The most likely causes of cracking and crumbling are the paint itself and/or bad painting technique. As discussed above, acrylics can certainly crack, but on the whole they are less vulnerable to cracking than oils.
  • Many of the paintings attributed to acrylic (including Rothko’s Harvard Murals) were done in other media. [28]

Summary

Fears have been expressed that there might be wholesale failures of acrylic paintings after they have aged longer. Acrylics have not been around long enough, and accelerated testing is not reliable enough to definitively prove that this won’t happen.

But to this author, it seems far more likely that acrylic paintings will prove very long lived, especially if they are properly painted with high quality contemporary materials and well cared for. The weight of available evidence indicates that acrylics will prove to be more durable than oils, and oils have been around for 500 years.

Acknowledgements

The author is grateful to the National Science Foundation for support of research on artist paints under grant number 9903813, “Artist Paints with Improved Durability.” Helpful comments from the artists’ point of view were provided by Professors Diana Pancioli and Roy Johnston of Eastern Michigan University. Valuable insights were provided by Mark Golden and Jim Hayes of Golden Artist Colors, Inc. Jodi O’Dell, also of Golden Artist Colors, Inc., provided excellent editorial assistance.

1 www.societyofcanadianartists.com/tips/acrylics June 30 2004.
2 www.artandantiques.net July 7, 2004.
3 www.wetcanvas.com/forums August 11, 2003.
4 R. Mayer, The Artist’s Handbook of Materials and Techniques, 5th Edition, updated by S. Sheehan, Viking, New York, 1991, pp. 209-211.
5 J.D. Erlebacher, M.F. Mecklenburg, and C.S. Tumosa, Polym. Prepr., 33(2) (1992) 646-647.
6 M. Mecklenburg, C.S. Tumosa and M.H. McCormick-Goodhart, “A General Method for Determining the Mechanical Properties Needed for the Computer Analysis of Polymeric Structures Subjected to Change in Temperature and Relative Humidity,” Journal of the American Institute for Conservation, (1994), Vol. 33, No. 2, Article 7, pp. 153-170.
7 Anon., “A special feature on acrylic and other synthetic media paintings, Part 3: Acrylics – inherent susceptibility to cracking,” McKay Lodge Conservation Report, 1991, No. 3, 16.
8 www.goldenpaints.com
9 P.M. Whitmore and V.G. Colaluca, Studies in Conservation, 40 (1995) 51-64.
10 P.M. Whitmore, V.G. Colaluca, and E Farrell, Studies in Conservation, 41(4) (1996) 250-255.
11 R. Mayer, op. cit., p. 503.
12 J. Mallegol, J. Lemaire, and J-L Gardette, Studies in Conservation, 46, (2001) 121-131.
13 J. Crook and T. Learner, The impact of modern paints, Watson-Guptill Publs., New York, 2000.
14 R. Mayer, op. cit., p. 468.
15 P.M. Whitmore, V.G. Colaluca, and E Farrell, Studies in Conservation, 41(4) (1996) 250-255.
16 Henry W. Levison, “Yellowing and Bleaching of Paint Films,” Journal of the American Institute for Conservation, (1985), Vol. 24, No. 2, Article 2 pp. 69-76.
17 Kenneth R. Sutherland, Solvent extractable components of oil paint films, 1, (2001)
18 Mark David Gottsegen, The Painter’s Handbook, 1993, p. 41
19a. Anon., ASTM D 5098. b. Anon., ASTM D 4302.
20 J. Crook and T. Learner, op. cit., pp. 21-24.
21 C. V. Horie, Materials for Conservation, Reed, London, 1987, pp. 92-96.
22 Other features of their chemistry are different. Car paints are highly cross-linked, and in the factory they are cured by baking at temperatures above 120 oC (250 oF).
23 T. Learner, Studies in Conservation, 46 (2001) 225-241.
24 “Artist Paints – An overview and preliminary studies of durability,” Jones, F.N.; Mao, W.; Ziemer, P.D.; Xiao, F., Prog. Org. Coatings, 2004, accepted for publication.
25 D.W. Grattan, Saving the Twentieth Century: The Conservation of Modern Materials, (1993) 411-438.
26 E.B. Wyer, “Flaky art; modern masterpieces are crumbling,” New York, (January, 1998) 25.
27 C. Hume, “‘Cracked’ painting row shakes art world,” The Toronto Star, (May 24, 1992).
28 C. Lees and R. Palmer, “Cracking paint ruins modern masterpieces,” The London Times, (March 29, 1992).
29 P. Recer, “20th-Century art fails the test of time,” Toronto Globe & Mail, (September 1, 1992).

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