My old airbrush teacher taught me years ago to cut costs when working large on canvas. Frisket paper is way too expensive, so here’s a great alternative. Use wax paper that you spray VERY lightly with photo mount adhesive. You can overlap edges to cover a very large canvas, do it in rows. That way when you spray, you cut out just what you need, and then you can recover it to work on another spot. It works! When you are cutting thru have a very LIGHT hand, you want to be careful not to cut the canvas. When I airbrush I always give the canvas at least 4 good coats of Gesso, sanding between coats for a nice smooth finish. That helps also when you are cutting into a frisket to not nick into the canvas, it’s protected. Hope that helps a little!