100 year old recipe I found on youtube: A pound of beeswax, cut up to speed melting. Then take it off the flame and add 8oz of boiled linseed oil and 8oz of turpentine. Stir continuously. As it becomes a paste scoop in to a sealable container. For use on canvas, leather, wood and metal. Waterproofs and protects.
First, A Bit of Oil You start by wiping on a very light coat of boiled linseed oil. Apply just enough to darken the wood and then wipe off any excess. When applied sparingly, the linseed oil will simply cure under the following coats of shellac and varnish. I like the way it brings out a beautiful, warm color in most woods. The change is immediate and pretty dramatic.
Oil Painting Medium, based upon recipes from the Old Masters. ***THIS is probably going to be the BEST link I'm going to find for what I want. She even mentions Gamblin mediums that she's used in the past. She uses the same 3 components, but changes the percentages from underpainting, to mid-painting, to the end of the painting---to make sure all is well in regards to "fat vs. lean" as the layers progress.