Sinking in is just awful. You put all this work in to making your painting a shining gem, and then twenty-four hours later it looks like complete crap and there's not enough wine in the house to convince you your art career isn't a lost cause. I can think of four ways to deal with sinking in:
- Oiling out: Not a great idea (whether your "oiling out" layer is oil or any other painting medium). Applying isolated layers of oil to your painting, which then become sandwiched between paint layers, is not great practice. It will lead to problems that get art conservators' panties in a bunch, like yellowing and delamination. I have to point out that in my vocabulary, oiling out is different from laying down an oil couche (French for "layer" and pronounced "koosh" in civilized parts of the world, "couch" in America, and "chesterfield" in Canada). Oiling out is when you saturate the surface of the painting with oil so that you can take a look at it. This oil then dries, and the next paint layer goes over top. Painting into a couche is when you oil out the specific area that you are going to paint overtop of that day. This brings back the colours so that you can see them and match them correctly (very important, especially around the perimeter of the area you are working on so that there is a seamless transition between today's work and the rest of the painting) and makes blending and fine detail easier. The oil that is laid down in a couche ends up being incorporated into this new paint layer and does not dry as an isolated oil layer, but helps make this new paint layer fatter than the previous layer.
- Retouch Varnish: During a studio visit once I saw a gorgeous portrait painting that had been retouched with spray Dammar retouch varnish in between each of about a dozen paint layers. The beautiful thing was cracking and flaking right off the canvas before the painting had even been completed. Similar to having isolated oil layers in between your paint layers, having isolated varnish layers is also a bad idea, and probably a worse idea, since varnish/resin doesn't have as much tensile strength/flexibility as oil. Hence the flaking and cracking in the beautiful portrait painting.
- Tackling sinking in before it happens: Using a painting support with a very low-absorbency surface or painting very fat will help prevent sinking in. Personally, I don't worry about sinking in enough to bother preventing it, but if, for example, I'm working on a painting in which a dark background is a very important element visually (ie, all my values have to be gauged off of that background) then I will mix stand oil into my paint on the palette before I apply it at a ratio of about 1:4 or 1:3 stand oil to paint (do not add OMS to the mixture to increase flow. This will make it sink in). This works really well. The only thing is that subsequent layers of stand oil-y paint need more and more oil added, as per the rule of painting fat over lean. There are other mediums on the market that seem to help prevent sinking in if you mix them with your paint. Like I said, I don't really care enough to bother and I don't like adding mediums to my paint if I can help it.
- Rublesol Light/Essential Oil of Petroleum: This is a zero-repercussion way to saturate the surface of your painting and make it look like it will when varnished, if only for about fifteen minutes. It gives you a chance to take a look at your painting, photograph it, restrain yourself from throwing it in the fireplace, or show it to a studio visitor. You can use it at any stage of the painting so long as the paint is dry. It will not leave any residue. It is also not a silver bullet. It's just a really useful tool to have in your arsenal. If you have some handy in your studio, you will eventually get to the point where you are using it almost everyday for one thing or another.