Most people know how an oil painting is done, but they usually don’t know that every oil painting needs a clear sealer to protect it from moisture, dirt, cigarette smoke, etc. Without a sealer, those things penetrate the oil paint itself can cause damage. If a painting was sealed more than 5-10 years ago, it should be examined closely. Over time, sealers can develop cracks, which, again, allow these contaminates to reach the paint itself. It’s also common for sealers to turn yellow and even light brown over the years; in this case, assuming there’s been no other damage, we’d simply give the painting a quick cleaning (to remove surface dirt) and reseal it, processes which are relatively inexpensive and should be considered normal maintenance.
Copyright Vicky Kornemann, 2010