@brdross I don't think walnut oil is used in manufacturing oil paint because it slows the drying time a lot, so if you use it as a medium while painting, use it sparingly. Typically, they use linseed or poppy seed oil for paint. The paint does not contain solvents in it, just oil as a binder that the pigments are ground with. Walnut oil can be used to clean the brushes too, but leaves oil on the brushes. There is also a citrus based oil for cleaning brushes, and that will also slow the paint drying time if there is too much of it left in the brushes. When I have left over solvent free gel medium at the end of my painting session, I use that to remove paint from the brush, then blot with paper towels, so there isn't much left to clean. That is when I use the "odorless" solvent, wipe off all I can, and then dish washing liquid and water to clean the rest off and let it dry. The solvent free gel is an alkyd medium that can be used with oil or alkyd paint and it speeds up the drying time and is a clear gel for thinning paint and getting transparent glazes. It must be removed completely in cleaning the brush so it doesn't dry and glue it all together. I hope that helps! Happy painting!

Jennifer