I have used Krylon Fixative spray at times to seal and restart paintings.
I think this is a terrible idea. Why do you feel the need to seal it? Adding a layer of varnish complicates the structure of the paint film and will most likely cause problems in the future, so it would make more sense to just paint straight over the top of the old stuff.
I hope that you are only using a very thin layer as a type of retouch, but even then, I can’t see what advantage it would give you.
Ron
www.RonaldFrancis.com
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