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.
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.