Q: Can I use denatured alcohol to clear the bloom on some old oil paintings?
A: Yes. Make sure the denatured alcohol has completely
evaporated from the surface, then revarnish the painting. The least
trace of moisture can cause the reappearance of bloom--that whitish
veil that grows over the surface a painting. Bloom is water vapor that
has penetrated the varnish or is trapped between the paint film and the
varnish. Varnishing on a cloudy or humid day can be enough to cause
bloom if the moisture in the air becomes trapped under the drying film.
Cracks or pores in the varnish film are another way that moisture can
penetrate the film.