• Michael Skalka

Testing the Test?

Summary: The ASTM subcommittee D01.57 creates standards that manufacturers may follow to assure their products are light fast, indicate the main ingredients and have appropriate warning labels if required. Other than D4236, the standard that formed the basis for the Labeling of Hazardous Art Material Act, all the other standards are voluntary. On occasion, questions arise about the validity of the subcommittee’s test methods and results. While test methods were meticulously constructed and repeatedly checked, if an artist encounters a problem with an art material, they appear to gravitate toward questioning the test results rather than the manufacturer’s choice of pigments, binders, etc., that make up the product. What is behind all of this?



I wish I had a better phrase to describe the process of creating a standard. Briefly, a standard is an instructional set of steps to be followed in order to collect data, analyze it and extract meaningful results. The work behind making a standard is to build a test method and then see if the test does what it is supposed to do. Basically, we embark on crafting a test and then test the test to assure it provides useful results.


Because ASTM subcommittee members are volunteers who mostly have other full-time careers we only meet periodically, to review and share information on tasks we are conducting. Standards take years to develop. Writing the text to the standard is an exercise in technical writing that demands razor-sharp precision. The ultimate goal is that accurate results following the test method should be attained by anyone reading and following the instruction set. A standard should not require a supplemental live instructor to walk a technician through the process.

Now that you know that bit of information about what we do in our subcommittee, lets move on to the heart of the matter. As said, questions come up periodically when an artist finds a failure point in an art material. The few artists who know about ASTM and our subcommittee, sometimes question the validity of our tests when we revise a standard or a round robin test reveals a fading problem with a pigment.

Art material problems can include binder-pigment separation, inconsistent color from one tube of paint to another and the most dreaded failure, color fidelity deterioration, or what most of us would call “fading.” You know it is bad when a color fades within the time a picture is started to when it shows signs of fading a year or two later. However, that is not the usually the case.


Most artists spot fading when an artwork is revisited after being in storage for a time period. The hot pink color applied to a floral still life does not have the same punch as it did when it was first executed. Sometimes an artist working in pastel will notice that the underside of a pastel stick does not match the side that was exposed to light.


So, a question is posed by an artist: “What is wrong with the ASTM light fastness test?” The answer is nothing is wrong with the test. The reason for fading is due to the manufacturer using a pigment that is sensitive to light and fades. Nothing complex to understand here. If a manufacturer does not have a quality control step in their company process for assessing raw materials and does not test batches of colorants, especially if their supplier is new or has indicated a change in formulation or additives, then the fault is with them, not ASTM.


Recall, news articles about aircraft maintenance companies using undocumented, “grey market” or downright counterfeit replacement parts. A whole ton of standards and painfully detailed guidelines exist for aircraft maintenance and the selection of parts. There have been disasters as a result of using counterfeit parts. You can’t blame the standards making organizations when someone deviates from the information published for the specifications of aircraft parts.


The same hold true for art materials. Giving credit to the art materials manufacturers, the landscape of pigments available is not an easy task to navigate. Raw materials are discontinued. Pigment formulations and additives change over time. New vendors emerge with no track record of selling stable, permanent colorants. Most manufacturers have long-term buying relationships with producers and they count on the homogeneity of pigment batches to remain the same. More established companies do quality control testing to assure that a new batch performs equally to the previous one.


In my opinion, I do not believe with the mainstream brands of art materials that oil paints, alkyds, watercolors, acrylics, especially the one company that complies with D5098, the acrylic paint standard are fraught with fugitive pigments in their products. I cannot say the same for pastels. Over the last decade, pastels were tested in a round robin (3 companies preparing samples using the same test method to assess the light fastness of a group of products) and about one-third of the 216 pastels tested, indicated light fastness problems that spanned a range from minor to severe.


Further, in my opinion, I cannot address the lesser-known brands, especially products that cannot be legally sold in the United States (products that do not have ASTM D4236 conformance statements) for the light stability of their products. What is even worse is that some non-conforming brands do not carry the US or EU hazardous warning labels required to sell them. See my essay on this subject by clicking HERE.

For years, members of the ASTM subcommittee have actively encouraged artists to paint out samples of the paints they use on a suitable support, cover half of the sample and expose them to sunlight for 8 months to a year. Uncover the samples and compare the exposed to the unexposed. This test is down and dirty but while it is not as precise and quantitative as an ASTM light exposure test, it can give a decent indication as to the light fastness of the materials you are using. If I were a pastel artist, I would absolutely do this test to check my pastels.


Well, that is enough behind the “curtain” discussion about the art materials industry for now. I will return next week to continue “colorful” stories about the origins of pigments and the history of science related to art materials.


In the time being, I am following the commissioning process for the Webb telescope. So far so good. The number of critical failure point tasks are decreasing. With luck and skill, astronomers will soon be looking back to the origins of the universe with an amazing new tool.


(Note: I am revising the format to include a summary at the top of the essay. This also helps when the Syntax articles are advertised on Facebook.)


The Syntax of Color

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