[OrangeAnalytic]

Yes, I'm familiar with the technique. Having studied the "Old Masters" techniques and materials many years ago with an artist's group in Southern California I can say that the technique originates from that era in Europe. They cooked up linseed oil with a particular percentage of white lead to make a soft transparent paste that worked excellent for blending into the next area to develop. What this medium gel was also about is that you could take a soft lint-free cloth and "erase" the day's work if you didn't like how things were looking. This medium is also geared towards the use of fanning brushes to create your brushstroke-free areas like backgrounding especially in your paintings. I have cooked up batches of this stuff, myself. Rabbit skin glue on stretched linen is a whole 'nother ball of wax.