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Acrylic Medium Sizing Test For Oil Paint

February 19, 2011

I’ve written a couple of posts in the past regarding tests I’ve made for sizing paper (it applies to canvas also) before painting on it with oils. One article dealt with using shellac and another with hide glue (aka Rabbit skin glue.) Here I would like to mention another option of using acrylic medium as a sizing barrier. My preferred brand is Golden’s GAC100 and that’s what I’ll be demonstrating here. The coats are applied without thinning with water.

On the left you can see a very thin sheet of paper taped down to a sheet of plastic. On one side I’ve placed two coats of GAC100, and on the right is four coats. After this sufficiently dried for about a day, I applied some oil to both sides. On the top is a strip of refined linseed oil by itself. Below that is a strip of Paynes Gray paint by LeFranc, and Cinnabar Green from Sennelier. I chose these two since they happen to be a bit oily as is from the tube and both use safflower oil. You can also see that the 4 coats of medium is more glossy than 2 coats in the picture on the right.

After only a minute or so, I held this paper up to a window and could immediately see that the oil strip on the top of the 2 coat side is already starting to penetrate into the paper (light spots.) I can’t really see any penetration from the paint oil, but that might just be because of the pigment or the amount of oil being used. Even a day later the 4 coat side showed no penetration at all, even from a generous amount of linseed oil.

The conclusion I gain from this test is to use at least 4 coats of acrylic medium as a proper sizing layer. If you only want the sizing barrier itself, then use 4 coats of that, or you could use 2 coats followed by 2 primer coats of an acrylic “gesso.” Golden specifically recommends their GAC100 as the best medium to use for sizing instead of other acrylic mediums which don’t prevent the oil penetration as well. In addition they also mention protecting against“surface induced discoloration” that might occur from the substrate itself to damage or stain the paint surface. 4 coats of primer alone would protect against oil penetration but not S.I.D.

These sizing coats work fine but are a bit slick for the first layer of oil paint. What I’ve done to remedy that is apply a thin coat of oil paint first of whatever color I wish, even white. I’d suggest using a linseed oil base paint for that layer instead of safflower or poppy since it’s a stronger oil. If you use a primer then that won’t be necessary. One tip to note is that an acrylic primer has a grittiness that can be brutal on brushes, so using 4 coats of sizing instead will avoid that problem.

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