Painting Teacher Question:

A phenomenon that occurs with varnish on paintings, and occasionally on polished furniture. Causes can include damp conditions during varnishing, picture hung in a chilly, draughty position, or exposed to gross humidity such as can be generated by some gas heating devices. The condition appears rather like the bloom on a black grape. If it is on the surface of the varnish it can normally be removed by gentle wiping with a piece of cotton wool. If underneath the varnish, which is rare, the only cure is to remove the varnish and to revarnish.