Lightfastness—a Matter of Longevity

63-lightfast-image.jpgThe lightfastness rating of art materials serves as an good indicator of how permanent our materials are. These ratings measure the general effect light has on them. The United States measures the permanence by the American Standard Test Measure (ASTM), with ratings from 1 to 5 with 1 and 2 being considered the most permanent. 

Currently, pastel manufacturers are working to get their ASTM ratings. Soon the pastel public will have the same information that oil, watercolor and acrylic painters have been enjoying. Since certain pigments are less permanent than others, it will prove helpful to have this rating available when choosing individual pastels. General pigment ratings have been around for a long time; the interaction they have with certain binders and fillers, used in the manufacture of the pastel sticks, has not been tested. Some unstable pigments when mixed with other very stable pigments and fillers perform very well, while other very stable pigments will perform poorly when mixed with certain pigments and fillers. Red is one of the most vulnerable color families in pastel; the best hues are often made with heavy metal pigments. Since pastel is a dry medium, easily made airborne, heavy metal-based pigments can be dangerous. This has led some manufacturers to use more fugitive pigments that are prone to fading. Knowing the lightfast rating of these individual sticks will allow us to choose the most permanent hues possible, adding to the longevity of our finished pastel paintings, and increasing the medium’s reputation.

It is not just our pigments that are susceptible to the effects of light. Pastel surfaces can be as well. Colored papers and pre-toned surfaces need to be scrutinized for their permanence and ability to stand up to years of light exposure. Many colored surfaces are similar to colored mat board used in framing. These are colored with dyes, instead of more expensive pigment-based colors. If you work in a fashion that allows a degree of the surface to show through, it is imperative that you understand its lightfastness rating.

If the manufacture of your favorite pastel brand or surface does not provide an ASTM lightfastness rating, you can easily make tests for yourself. In fact, these are wise to do even when the ratings are available. Start by taking the surface you wish to test and place strong pastel marks from the individual sticks you want to test (making note of what they are). Place an opaque strip of cardboard across a portion of the test sheet. Place the test sheet in a sunlit window for a couple of months (see my example above). At the end of the time frame, remove the opaque strip and analyze the effect light has had on the exposed area. If there is virtually no difference, you are using the most lightfast materials. If there is considerable change, you need to rethink some of your choices. We owe it to the purchasing public and ourselves.

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3 thoughts on “Lightfastness—a Matter of Longevity

  1. Michael Skalka

    The standard for testing lightfastness of pastels is in progress. Until the draft of the standard comes forward for balloting by the subcommittee, no evidence of work being done on that standard will appear on ASTM’s website. While the process of creating standards is obscure, the work of the subcommittee is not. Anyone interested in attending or becoming a member of ASTM’s subcommittee on Artists’ Materials D01.57, can participate in the work we do. As with all other art materials, ASTM will create a standard for testing pastels so that manufacturers will be able to rate them as a part of the fabrication process. Our subcommittee will not be preparing a list of acceptable verses unacceptable pastels in terms of lightfastness. We create the tools for manufacturers to do the test so that all work from a level playing field.

    The art societies should have a presence in ASTM. That is not the case right now. We have so few artist members that the do not play a key role in creating the testing procedures. Unfortunately, so much of the work of this subcommittee is technical and most artists do not have the science and materials testing background to help create the body of the standards. However, they can play other roles in promoting the manufacture of high quality art materials and their participation is always welcome.

    CPSA took a very active role in creating the pencil standard. It does take time because all members of the subcommittee do this work as volunteers and their regular jobs slow the progress of writing standards.

    Regardless of getting a standard or not, I am very concerned that even if we do enact a standard, the practicing artist takes very little interest in the work of ASTM. That was evident when the pencil standard came out. Manufacturers made lightfast lines of pencils only to have then ignored by the colored pencil artists. Some already have been discontinued because sales were so poor. So between manufacturers and the CPSA, no aggressive marketing was done to inform artists that colored pencils made to meet the specifications of the standard a positive thing for artists.

    I encourage you to get involved in ASTM and either join or state your interest in learning more about the work of the subcommittee. Email me at with your questions about participating in the work of D01.57.

    Michael Skalka, Chair, ASTM D01.57 Artists’ Materials

  2. Richard McKinley

    The ASTM ratings are being done. I spoken with Terry Ludwig, of Terry Ludwig Pastels, and they have their rating. The buzz is that most of the others are in the works, close to complete, or done. It does appear to take time and I am sure that all the info will be coming out soon. In the meantime I recommend contacting the individual pastel companies for more information on their ratings.

    Even with the ASTM rating it is wise to do some of your own testing – never hurts!

  3. Katherine Tyrrell

    I was very interested in your comments as my understanding is that there is no ASTM standard for pastels in existence. (See the relevant ASTM ARTISTS’ PAINTS AND RELATED MATERIALS STANDARDS web page and ASTM D4303 – 06 Standard Test Methods for Lightfastness of Colorants Used in Artists’ Materials

    I can’t even find any ASTM evidence that this is being worked on – but maybe you know more than me….?

    I’d really like to see the Art Societies, which have leading professional pastel artists as members, taking a much higher profile in pressing the manaufacturers to make some progress in this area with ASTM.

    This approach worked in the area of coloured pencils and CPSA has a lot to be proud of in that regard. However it’s taken 5+ years to see real progress since ths standard was approved – and the job is still not finished.

    I’m really not quite sure why we haven’t seen the same sort of leadership role adopted by the national and international pastel societies.

    Will it take pastel artists doing their own tests – as per the suggested ASTM generic standard – and announcing the results on blogs and in forums to start seeing some movement in this area?