1. First paint the frames to match (if they don’t already). Spray two coats of primer, then two coats of paint. Let dry about an hour between coats.
2. While the paint is drying, measure the opening of your large frame. Using the ruler, self-healing mat, and utility knife, measure and cut a piece of the cardboard to fit. Mine was 11×14 inches. Then measure the opening of the smaller frame, then cut a hole the same size in the center of the cardboard.