Q: How often do I have to varnish an oil painting? How do I clean the painting before I apply new varnish?
A: A final coat of varnish—on a finished and completely dry
oil painting—can last hundreds of years. Sennelier makes two kinds of
varnish for works in progress, one of which is called Turner Touch Up
Varnish, which dries quickly. It is designed for restarting an oil work
on a dry base and to correct for sinkage. It can be thinned with
turpentine or mineral spirits. The other kind of varnish is also called
Touch Up Varnish but includes an alcohol base. It is a clear, synthetic
resin that does not yellow, dries quickly, and can be thinned with
alcohol. It is recommended for professionals and art restorers due to
the delicacy with which it can be used.
If you are cleaning your own painting, I assume that the painting
has accumulated layers of environmental residue. Do not use any soap
solution because this can damage your painting. If moisture gets under
paint, it will create a bloom. If your painting has any mold, exposure
to strong sunlight (or ultraviolet light) and fresh air usually
destroys it and stops its growth. You can also use a water-dipped
cotton swab in a gentle circular motion to clean small areas of a
painting.
--by Camille LaPointe-Lyons
Q: What is the best process for applying varnish to a large
oil painting? Should I apply a retouch varnish to protect the painting
until it is time to apply the final varnish?
A: Touch-up varnish keeps the paints unified while you are
working on a painting. It will mask sinkage, brighten colors, and
provide an anchor for fresh paint when resuming a work that has already
dried. Touch-up varnish should be used on only the small area of the
painting that you are working on. Once your entire painting is
complete, it can be applied in a thin coat as a provisional varnish
until your painting has completely dried. This will take six months to
a year to cure, and then you can apply the final varnish.
There are two types of touch-up varnish: solution varnish, thinned with
alcohol, and cooked oil varnish, thinned with mineral spirits. Final
oil-painting varnishes should only be applied to completely dried oil
paintings, and the paints will take a year to completely cure. You will
also want to consider whether you want your varnish to have a matte,
satin, or gloss finish. Be sure to paint thin layers of varnish on the
painting with a very broad, soft bristle brush, and keep the painting
almost flat to prevent beads of varnish from running across your
painting.
--by Camille LaPointe-Lyons