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Blocking Support Induced Discoloration

Support Induced Discoloration or SID describes a phenomenon that can occur when the acrylic appears to change in color upon drying. It usually takes on a yellow, orange or brown tint, due to impurities in the substrate being drawn up into the acrylic film. The discoloration occurs while the paint or medium is drying and curing and should not continue or happen after the film is cured. This can be found in supports including woods, hardboards, particle boards and some canvas and linen supports. These impurities can include glues, resins, sizing and any soluble materials in the substrates. SID is only applicable when painting with acrylic paints and mediums and most noticeable in thicker applications of clear or translucent mediums and gels and in opaque and semi-opaque pastes. It can affect some paint colors as well.

In 1989, GOLDEN partnered with the Art Conservation Department at Buffalo State College to try to understand what was causing a fast yellowing or browning of a matte acrylic film on canvas. Through an error in the testing of a small corner of acrylic gel becoming detached from the canvas and remaining clear, it was determined that the substrate was causing the discoloration and not just the acrylic film changing color on its own. The term Support Induced Discoloration or SID for short was then coined. (1)

Our recommendation to block SID on these substrates has historically been GAC 100, but recent testing has shown that our Gloss Medium is more effective and we have changed our recommendation to reflect that. As you can see in the image below, applying 2 coats of Gloss Medium directly on the support before applying any other product, is most effective in blocking SID from the thick application of Regular Gel Gloss. In the case of OPEN Gel Gloss, which has a very slow dry and curing time, the wet product lingering on the surface allows more impurities to be drawn into the gel and the Gloss Medium is less effective. This is a “worst case scenario” test, as we only recommend painting with OPEN products thinly. It should also be noted that Gloss Medium and GAC 100 do not seal wood, they really just serve to block SID. Washing the canvas before painting can be somewhat effective, but usually this results in a wrinkled fabric and it can be hard to rid of all of the wrinkles, even when stretching. Washing linen was less effective to stop the Support Induced Discoloration. (2)

Top Row: Regular Gel Gloss, Bottom Row: OPEN Gel Gloss.
From left to right: No sizing and Gesso only, One Coat of GAC 100 then Gesso, Two Coats of GAC 100 then Gesso, One Coat of Gloss Medium then Gesso, Two Coats of Gloss Medium then Gesso

More information on Support Induced Discoloration can be found here in the video Support Induced Discoloration (SID), what is it? and how to minimize it: https://vimeo.com/273304693 and on the goldenpaints.com website here: https://www.goldenpaints.com/technicalinfo_prepsupp or by contacting GOLDEN at 800-959-6543 or by emailing us at help@goldenpaints.com.

(1) , (2) Hamm, J, Gavett, B, Golden, M, et al., “The discoloration of Acrylic Dispersion Media”, Saving the Twentieth Century: The Conservation of Modern Materials, Canadian Conservation Institute, 1991, 381-392

10 Responses to Blocking Support Induced Discoloration

  1. David Randall June 26, 2018 at 1:53 pm #

    Are you recommending the gloss medium be used over acrylic primed canvases?

    • Stacy Brock June 26, 2018 at 1:56 pm #

      Great question. We are currently doing tests to see if the Gloss Medium would work to block SID on top of Gesso and will revise the article to include the results. We suspect that there would be very little SID with a pre-primed canvas in general. We see more if this occurring with wood and particle board panels.

  2. Sylvia Oates June 26, 2018 at 4:32 pm #

    What about canvas that has been primed with gesso?

  3. De Barnett June 26, 2018 at 10:15 pm #

    What can you use to prevent SID on a pre primed canvas if gloss medium only works on non primed surfaces? Can you mix gloss medium with white gesso and put a coat before painting to prevent SID, or put a layer of gloss medium on preprinted canvas and add another coat of gesso over the top?

  4. Lisa Pendrys June 30, 2018 at 10:30 am #

    Using the technique described above to use Gloss Medium as a primer with wood, is there a sealer you recommend for wood, such as birch board, etc? Or can one use any product like Kilz Max (Ph 5-8) or something else? I am embarking on a project using large custom cut, high quality birch boards from a local wood working shop & need to figure out what my best choice is for a sealer. After I seal, I could cover with Gloss Medium. My next steps are an acrylic layer or two, then oil & cold wax. Thanks for any pointers.

    • Stacy Brock July 9, 2018 at 4:02 pm #

      Hi Lisa,

      If blocking moisture to the wood is your concern, you could prime with an alkyd primer. Support Induced Discoloration is only an issue with acrylic paints, so there would not be a need to use the Gloss Medium on the wood if painting in oils. We generally recommend either 3 coats of Gesso or Fluid Matte Medium (if you would like a Clear Gesso) directly on panel, linen or canvas to block oil penetration before painting with oils. Here is an article about preparing panels for a life outdoors that talks about alkyd primers on wood panels: http://www.justpaint.org/preparing-panels-for-a-life-outdoors/

      We hope this is helpful and if you have any other questions, feel free to email us at help@goldenpaints.com

  5. Lloyd Goodwin June 30, 2018 at 3:52 pm #

    I have often used a gloss medium sealing coat (usually tinted) over canvas that has only one coat of gesso. I haven’t noticed discoloration in the sealing coat. Since I usually paint the whole canvas I don’t worry. Even if some discoloration occurred it doesn’t seem to migrate into upper layers.

    • Stacy Brock July 2, 2018 at 6:04 pm #

      Thank you Lloyd for sharing your experiences. That is very helpful!

      Best,
      Stacy

  6. Lloyd Goodwin June 30, 2018 at 3:56 pm #

    How much raw canvas area can be covered with two coats using a 128 oz. jug-o-medium?

    • Stacy Brock July 2, 2018 at 6:08 pm #

      Hi Lloyd,

      It is really dependent upon the absorbency of your surface and how thickly it is applied. A very rough estimation would be around 300 square foot per gallon, but you can do a more precise estimation by testing yourself. The details can be found in this article: http://www.justpaint.org/estimating-square-foot-coverage-for-products/

      Best,
      Stacy

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