In the last year my sample set for violin varnish ground coat tests has grown to about 40. I don’t feel like I’ve solved anything, but from the samples, and my observations of old instruments, both in my hand and through the microscope, have given me a full set of criteria that a nice varnish ground needs to meet.
At the top of the list are two things: sparkling wood fibers when lit from any direction, and maximum transparency–the ability for the microscope to see down through layers of wood cells into lower layers, which depends on very transparent wood structure. On older Cremonese violins that is much more the case than on anything new that I’ve seen.
