Q: I want to rework an oil painting that has been sitting for more than a year. How should I go about it?
A: Begin by cleaning the canvas surface. Wipe away any dust
particles with a cotton cloth or with cotton balls. If any dirt is
evident, remove it with a very small amount of turpentine. Then apply
retouch varnish to the absolutely dry surface with a soft brush. This
will create a uniform wet appearance, making it possible to match
colors. Retouch varnish should always be applied in very thin layers.
Here’s a simple recipe for retouch varnish: Add 8 oz of turpentine to 4
oz of 5-lb varnish.