Use Dick Blick's Matte Acrylic Varnishes over Blick Matte Acrylic Paint, or any other craft acrylic paints. They provide a tough, non-yellowing protective coat.
Gloss Varnish — For a glossy finish, use Blick's Gloss Varnish. It is also clear, non-yellowing, and resists chemicals, heat, and abrasion. Cleans easily with water. 2–6 coats recommended. Plastic bottle.