Proper priming

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Proper priming

From Virgil Elliott

Published before 2005


Jeffery LeMieux wrote:
What do you suggest to use to "clean" the acrylic primed surface after it has "cured," and how long does it take for an acrylic primer to cure?

What can happen when any water-soluble primer like acrylic emulsion "gesso" is used on cloth or wood supports is a phenomenon known as SID, for support-induced discoloration. Certain water-soluble components in the support migrate through the ground layer(s) and cause it to change color. This can be prevented by applying a sizing to the canvas or wood support, and letting it dry thoroughly before putting the acrylic primer on top of it. However, rabbitskin glue is problematic in its own right, and is probably not the best thing to use for sizing, at least on stretched canvas. It is hygroscopic, meaning that it reacts fairly drastically to changes in humidity by shrinking and expanding, which caused changes in canvas tension. Oil paint films can withstand this while they are young and flexible, but eventually they lose their flexibility, and that is when delamination can occur. A better choice for sizing is a neutral pH PVA or an acrylic gloss medium thinned by half with water. Gamblin sells a PVA size ready to use, and Golden has an acrylic size that is well suited for the purpose.

Compounding the difficulties, where oil paint over acrylic primer is concerned, is the fact that there are surfactants, flow improvers, and other additives in acrylic primers that migrate to the surface as the primer dries and cures, which, unless cleaned off, can interfere with adhesion of oil paints (but not, it seems, with acrylic paints on acrylic primer). Most users do not bother to clean the surface before beginning to paint, nor do they allow enough time for the primer to properly cure, and that also can cause poor adhesion. The chemical dissimilarities between acrylic primer and oil paint prevent a chemical bond from forming, so the bond is mechanical only, which, at best, gives a bond that is approximately 80% as good as that of oil paints to oil primers. This might well be sufficient, at least on rigid panels, but there is some question of whether it is going to prove problem-free on stretched canvas over the long run, after the oil paint film has lost its flexibility. Golden Acrylics is currently conducting some experiments to shed more light on all of this.

So adding a coat of oil primer over acrylic primer might well result in delamination at the interface between the acrylic and the oil primer. I have had this happen on one painting. Fortunately, it was the only one I had ever tried that way, and it was a workshop demonstration, so not of great importance to me.

All of these concerns can be made less critical by attaching the canvas to a rigid panel, so it cannot flex.

Virgil Elliott