I did some tests a few years ago and varnish on plain canvas significantly weakened the skin. I could easily tear it with my bare hands. I don't know what effect varnish will have on a painted skin, but if the varnish penetrates the canvas, it makes the fibers brittle.

Mike

: Not sure that you will want to varnish over canvas, painted or otherwise.
: Varnish tends to be a rather brittle finish when hardened and the canvas
: will want to flex some. You may want to make a test panel, stretch it,
: paint it and add the varnish and allow to dry, then do some pushing and
: proding to see how it will hold up when flexed. ??? "Food for
: Thought"

: Rehd