Varnishes for Acrylic Painting
Varnishes are designed to protect an acrylic painting from the dirt, dust, and grime prevalent in air. Over time, any painting is exposed to pollutants that become trapped in the surface of the work. To clean the artwork is impossible unless the piece was properly varnished upon completion.
Varnishes are removable by definition, otherwise we call them topcoats. The proper way to clean an acrylic painting involves the removal of dirty varnish - so a topcoat will not suffice. Acrylics have a relatively open chemical structure which makes them especially prone to capture dirt from the air, thus varnishing is even more important.
Modern synthetic varnishes are not prone to yellowing or darkening, and come in gloss, matte, and satin finishes. An isolation or topcoat applied before varnishing will make make the varnishes easier to remove, and the cleaning process feasible.