Protecing while correcting your work
If you have an uncertain spot on your almost finished painting and you want to try and correct it but you are afraid of ruining the rest of the area, give it a coat of glaze medium.
That sort of seals off the area around and gives you a chance to make minor corrections. This is applying glaze medium to a dry painting , then allowing the glaze medium to dry before you start correcting. The glaze medium I use dries the same as my paints, so therefore I do not end up with dull and shiny spots