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Gesso Survey Results Insightful for Subcommittee

Nearly 300 responses to Just Paint 4's Gesso Survey for ASTM Subcommitee on Artist Materials!

Many of the artists who took the time to complete and return the Gesso Survey we ran in Just Paint, Issue 4 also used that opportunity to ask questions and make comments about our products, Just Paint, etc. There was also a lot of interest in finding out what the results of the survey were. To the nearly 300 people participating, thank you. Herein are the results of the survey, followed by responses to frequently asked questions and other comments that were made.

The Purpose of the Survey
The purpose of the survey was to collect information on current practices of support preparation. The size and priming layers of paintings are a critical interface between the support and paint layer. Acrylic gesso is a popular ground for both oil and acrylic painting. This has created interest among members of the Artist Materials Subcommittee of the American Society for Testing and Materials (ASTM), to produce a voluntary quality or performance standard for acrylic gesso. There currently are several ASTM standards relating to artist materials. For example, "Conforms to ASTM D 4236" on a product’s label means it has been evaluated and labeled for potential acute and chronic health hazards. There are also ASTM quality standards for different types of artist media, including Acrylic (D 5098), Oil/Resin-Oil (D 4302), Watercolor (D 5067) and Gouache (D 5724) paints. Manufacturers’ labeling their colors as conforming to any of these are voluntarily providing assurance to the consumer that the paints meet criteria for lightfastness testing and labeling as well as disclosure of the pigments used. Use of these standards allow artists to choose materials that are of the highest archival integrity.

By understanding where and how acrylic gesso is used, application practices, and attributes im-portant to artists, an ASTM Acrylic Gesso Standard can be designed that will address as many needs as possible. This will not result in one generic product, without brand differentiation, that will be suitable for all applications. Conforming products can still enjoy a unique balance of individual characteristics such as sandability, color, absorbency, texture and application characteristics. However, if universal properties are appropriate, such as lightfastness, stability or use of 100% acrylic in "acrylic" gesso, then all products in conformance will be of similar quality. It is the general theme in developing ASTM quality standards for art materials to concentrate on factors contributing to archival integrity while leaving ample room for individual variations in products. With the variety of supports and media being used, every conforming product will not be suitable for use in all applications. A more appropriate result would be for the manufacturer of the conforming product to provide clear and accurate label recommendations based on product testing under different scenarios of use (as demonstrated by the surveys). For example the Standard could require that if an acrylic gesso is to be recommended for oil painting, it must meet certain requirements for intercoat adhesion and instructions for use must describe the application parameters necessary to prevent oil penetration to the support.

Benefits of ASTM Standard
The primary benefit of developing this Standard within ASTM is that the committee is a group comprised of members from many perspectives. Working together on this project are artists, art material manufacturers and conservation scientists.

From this latter group, we expect help answering the more difficult questions, those dealing with the aging characteristics of works of art as influenced by the diversity of the materials used in their composition. To do this, the project plan calls for artificial aging of samples, followed by controlled degradation studies at conservation laboratories. Another important study would focus on the mechanics at the interface between paint layers of different chemical composition, such as oil over an acrylic ground. The net result of this work is hoped to be the identification of the "ideal" combination of support, size and ground for a given type of paint.

Summary of Survey Responses
1. Regarding the media artists paint with, we heard from users of most types of paints, including Oil, Acrylic, Watercolor, Gouache, Encaustic, Inks, Casein, Urethane, Egg Tempera and Pastel.

While the nature of our mailing list influenced the response, 30 percent paint primarily in acrylic, 5 percent in oil, and most of the rest use some combination of oil, acrylic and watercolor.

2 & 7. Just over 90% reported they Stretch and Prepare their own supports, with canvas the most popular, followed by rigid supports and then paper.

About 30% also reported using commercially preprimed canvas (Asked in question 7).

3. Over half of the oil painters responding report underpainting their oil paintings with acrylic.

In general, there are concerns that this approach may lead to premature loss of adhesion of the oil paint because the acrylics may lack sufficient tooth to ensure a good mechanical lock between the paint films. Acrylic gesso is different because it is formulated to provide a toothy surface which promotes adhesion.

4 & 6. Do you size? We defined size as "a dilute solution of material applied to porous supports to prevent absorption of paints". This is most relevant in regard to oil paints, where the support should be protected from absorption of oil, the acidic nature of which may cause deterioration. A "size" under acrylic paintings is also useful, if painting thickly in relatively transparent passages, to prevent Support Induced Discoloration, which is caused when the water and surfactant from acrylics wash materials from the support and allow them to migrate to the paint layer and discolor the painting.

Just over one half of all painters indicated they do not size. About one third of acrylic painters report sizing, most use a polymer medium.

A few painters indicated using rabbit skin glue. We recommend against this practice because rabbit skin glue remains permanently water-soluble. Under conditions of high humidity, a porous support such as canvas allows moisture to enter the glue layer which leads to swelling, followed by contraction as humidity drops. These cycles may lead to adhesion failure. Lack of flexibility of hide glue also makes it more susceptible to cracking from mishandling, and these cracks may transfer to the upper layers of the painting.

It was interesting to learn that most of the oil painters responding do not use a size. In addition to blocking oil penetration, a size functions to stiffen a flexible support, providing greater working resistance to the brush by removing some of the "bounce" of the stretched fabric. A stiff, permanent size may also decrease the likelihood of crack development by enhancing dimensional stability of the fabric against stresses resulting from changes in ambient conditions and shipping and handling. Our testing has shown that applying a sufficient number of layers of acrylic gesso will prevent oil penetration through to the support, but does little to stiffen it. There would still be benefit, when oil painting on flexible supports, from applying a size. For this, we recommend GOLDEN GAC 400, an acrylic polymer medium that is considerably less flexible than most.

5. Do you prime? The vast majority of painters responding to the survey report priming with acrylic. About 7% use lead based primer for some applications and 2-3% use housepaint. The prevalence of using acrylic gesso, particularly in combination with oil paint, underscores the desire within ASTM to be able to provide more definitive answers to questions regarding the best attributes for an acrylic gesso and how the materials will stand the test of time compared to traditional oil grounds.

8. For important attributes, resistance to changes in heat and humidity was ranked as the most important characteristic of a primer. This was followed by, in order of decreasing importance; flexibility, opacity, ease of application, lightfastness, surface texture, brightness, absorbency, price and transparency.

9. Have you noticed delamination? This question was asked in order to help determine the extent and type of failure related to primers and sizes. While there were numerous responses indicating that some form of delamination was observed, most either between the support and primer or the primer and paint, insufficient information was received regarding the types of materials used to allow us to identify key problem areas. absorbent Gesso, as required by watercolor artists, we recommend GOLDEN Absorbent Ground, available in either White or Canvas Color. This is formulated to be exceptionally absorbent, similar to using watercolor paper. The degree of absorbency is determined by the number of layers of Absorbent Ground applied.

Another frequent response on the Survey was a desire for a textured Gesso. Those requiring this may want to try GOLDEN Acrylic Ground for Pastel, which was designed to provide sufficient tooth for uniform laydown of pastels on any prepared surface. This product is translucent so it reveals the underlying surface. If desired, it can be applied over standard Acrylic Gesso or colors. Another effective way to achieve a more textured surface is to combine GOLDEN Gesso with GOLDEN Fine Pumice Gel or GOLDEN Coarse Pumice Gel.

Finally, for those people indicating they need a surface that can be sanded to a very smooth finish, we recommend GOLDEN Sandable Hard Gesso. It is available in white only and is slightly more absorbent than our regular Gesso. It can only be used on rigid supports due to a tendency to crack when flexed, but can be sanded to a highly polished surface.

The responses to our Gesso Survey emphasized that one product cannot be designed to meet everyone’s needs. In most applications, a traditionally opaque ground is called for, but sometimes a transparent ground that seals the support and provides enough tooth for subsequent paint layers is required. Differences are also desired in color, texture and viscosity. Preference for a highly sandable surface often outweighs the competing attribute of flexibility. These needs can all be effectively met, not with one product, but with selection of one from a variety of products or combinations thereof. It remains important that the user understand the limitations and the attributes of each particular material; for example that oil can seep through porous acrylic ground, that Sandable Hard Gesso can crack if flexed, etc. Support preparation is a key factor in how well a painting will age. By tailoring the product to the application, the requirements of the artist can be met while ensuring that the need for structural integrity is addressed.

If you would like to sample any of the grounds, mediums or gels mentioned in this article, or have questions or comments in regard to this information, please contact us at Golden Artist Colors, Inc.

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