I wanted to demonstrate how effectively shellac performs as a sizing medium for painting oils on paper. The shellac mixture below was made about half a day before the demonstration was started.
This is de-waxed pale “blonde” shellac in the bag. I ground it down into a powder to help accelerate the dissolving process. I tend to make my shellac in a rather unorthodox manner than what is normally recommended by first making a “soap” using dissolved borax. That is how shellac based ink is made. It’s approximately 1 teaspoon borax, 8 tsp water, and 5 tsp shellac. I can’t tell you the exact amount since I tend to do it by sight these days instead of careful measure. I place this in a jar and set it on a coffee warmer while stirring for a few minutes until all the water is gone and I’m left with a paste that looks like light brown sugar (see below.)
Next I mix in grain alcohol. Most recommended mixtures just start with dry shellac and alcohol and avoid borax, which is perfectly fine. I just found that it takes longer that way and doesn’t give a better result. The alcohol I use is the Everclear brand which is 190 proof. Denatured alcohol would work fine, but also takes longer. Keeping the jar on the warmer, I occasionally stir the contents and after about 2 or 3 hours I get something that looks like creamed coffee. The amount of alcohol is again not precisely measured but roughly about the same as the “soap” volume I started with. It amounts to what is referred to as about a 3 pound cut of shellac to alcohol. I’ve also used a 2 pound cut, but I would want to add a primer layer to that. Acrylic primers adhere fine to shellac but I wouldn’t recommend thinning them with water.
In the image above, on the left you can see the linseed oil and stand oil on a piece of the same paper that has no sizing protection, as well as a couple oil paints from Le Franc, red ochre and Paynes grey, which I believe use safflower oil. The oils started to soak into the untreated paper immediately, and when you look through the back (right image) you can see how the oils make the paper nearly translucent. As these oils dry they will release acid that will discolor the paper and likely make it brittle over time. Shellac prevents that.
The paper used above is thin bristol, about 90-100 pound weight. I’m using a thin paper so that any oil that penetrates through the shellac would be easy to see. I placed two coats of shellac on both sides of the sample paper and let that dry for about an hour. Next I placed three oil medium swatches of refined linseed oil, stand oil, and safflower that I had handy.
All of these were made about 5 days ago. In the image below (looking at the paper from the back) you see how the shellac has held up after that period of time and the oils have dried. None of the oil has penetrated through to the back side of the shellac treated paper.
Shellac is excellent sizing protection for oils and paper as well as wood. I prefer it to other choices. It does take some time to prepare, but it doesn’t require the use of water that acrylic mediums or animal glues would need, so there’s no worry about wrinkled paper. Rabbit skin glue has to be made at least a day in advance, whereas this sheet was ready for painting from start to finish in about half a day. An acrylic medium would be faster to apply, but the paper has to dry completely, requires taping down the paper, and I just don’t like the feel of oil paint on acrylic. A batch of fresh shellac will last at least six months or more. I keep it in the fridge until needed.