I started using the propolis on violins I have made. I buy raw bee propolis, which is scraped from bee hives. The bees produce it to seal the hives.
Dissolved in acetone, a yellow-brown varnish floats on top of the bees wax and junk. I brush on the thin varnish, and it really soaks into the wood and helps seal the grain. It also acts as a presurvative and smells good too. It also gives a slightly yellow stain to the wood, and acts as a good ground for the finish.
I let the propolis dry for a day or two, and then rub in several coats of boiled linseed oil.