Walnut Oil: Prefered Medium of the Renaissance

I may be more of a renaissance woman than I thought. I was running out of painting medium when I bought a bottle of walnut oil at the grocery store to tide me over and I’ve never gone back. Walnut oil cleans my brushes without drying them out and is not toxic or stinky like turpentine.

 “Grind the colors with walnut oil or linseed oil, 
though walnut oil is better because it yellows less over time.”
Vassari on Techniques, 1550

M. Graham & Co. Makers of Professional Artists' Colors and Mediums, create their oil paints with walnut oil... “Preferred by artists for over five centuries oil color ground in walnut oil provides rich, vibrant color with greater freedom of control over all types of painting application. Free flowing and slower drying, walnut oil enables delicate passages of finely blended color, rich jewel-like glazes or juicy full brush application with no addition of solvents. Because of walnut oil's unique refractive index and non-yellowing nature, colors ground in this fine oil are naturally more alive and brilliant. They retain their clarity and are free from the discoloration associated with other drying oils."
 

 Did Raphael achieve his juicy jewel like colors with walnut oil?