did the old masters varnish their works? what problems are there if you do not varnish?
THIS IS A DOUBLE POST. SEE OTHER THREAD TO RESPOND.
Yes the old masters did relay on varnish to preserve their paintings. In fact most of them to the middle of the renaissance have used "egg tempera" which needed to be varnish in order to be preserved. Problems ? They are many.
Visit some restoration I have don on ikons
caricatures from photo
Today there is absolutely no technical need to varnish oil paintings. In the past that was important as the permanence of paint properties was poor.
The main reason to varnish today is aesthetic. Sometimes it is good to varnish locally dark areas where it is complicated to check the tone.