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Friday, August 29, 2014

Panel Edges

Recently, we had a question about SID effecting the paint on the panel edges.  An artist was concerned about paint on the edges of the untreated panel, not cradle, and how that might effect his work long term.  Below, Dana Brown answers the question.

"The condition of SID is one of acrylic paint and acrylic dispersion ground (acrylic gesso). We make broad recommendations to sealing the painting surfaces of wood, as a separate step from priming, primarily due to the common use of acrylic gesso as a primer, but also to maintain a painting surface that is as acid-free as possible. It is also based on an understanding that proper habits can become good practice when using various materials. We know that sometimes artists will pick up a piece of wood to use as a substrate, not knowing its density or acid-level, and sealing the panel will give the painting a 'fighting chance,' of lasting.

Because of the differing characteristics of each paint type mentioned, I will address each separately.

Acrylics dripped over the edge (that thin, 1/8” thickness) will encounter some level of acids. It will also take on a level of discoloration. Support Induced Discoloration (SID) is not a dark blackening or even a dark browning of the paint film, and it is generally only noticeable in areas of white and generally only in the wettest of applications. This is why it is commonly associated with the applications of acrylic gesso, applied directly onto a wooden support. Areas of color mixtures or darker colors, especially when applied undiluted or more thickly, will not display noticeable discoloration in the same sense. If the entire acrylic painting is done onto an unsealed wooden surface, the levels of acids in the wood (which vary greatly from wood species and type) can cause damage to the artwork. The amount of acid or discoloration from a 1/8” edge is very small and will not put the painting in jeopardy of lasting or any continuous damage. The acid level in our hardboards is nearly neutral at that, and it is one of the reasons that we selected aspen as the overlay for our product. To sum up in reference to acrylic paint, if the drips or painted edge are white, applied quite wet, or thinly, discoloration may be noticeable. To prevent this, you can apply GAC 100 or PVA Size to the edges to create a barrier seal to the exposed, cut edges. For most painters’ practices, the effect of a few drips over the edge of a 1/8” thick panel is not damaging to the artwork or its appearance, and its durability is not at risk.

Gouache and oil colors are not susceptible to SID and the reason to carefully seal the panel before priming is again a rule of thumb, put forth by the general practice of acrylic dispersion grounds and acrylic based priming layers. The main issue with gouache dripping over the edge or being painted on the edge of a dark, brown panel is mainly that the edge may not be sufficiently absorbent to give a lasting mechanical bond between the paint and the panel’s edge. Also, the dark, brown tone may cause paint applications to look darker, requiring multiple applications.

For oil colors, there is also no risk of SID. The risk is more of great amounts of oil paint, directly applied to wood, soaking into the wood and oxidizing within the structure of the wood. This is even contentious amongst art conservationists and may be less of a risk than previously believed. The 1/8” thick edge of a panel will not allow for a risky level of oxidation within the wood support. The oils in oil colors will actually pass on some conditioning or preservation qualities to the wooden support, similar to applying oil to wooden furniture to recondition it."

-Dana Brown
Artist & Customer Support at Ampersand

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