AHA. Below is the URL that talks about an exhibit of watercolors made by Charles-Frederic Soehnee, none other than the famous maker of vernis soehnee which the article says is still used. Does anyone from France see it in stores today? Apparently he made his fortune on the varnish! I wonder if anyone has done a chem analysis of it?
Also a French book mentioning it on p. 350 that you can download...it is an 1844 volume scanned by Google, out of the Harvard Library. You can download it to your desktop and check out the couple pages on Soehnee which are pp. 350-1 in the book but I think, say, 367 in the PDF. Traite de chimee appliquee aux arts.
Enjoy your read (in French).
Christina Z. Anderson
Photo Option Coordinator
Montana State University