Masterpiece Tight-n-Up Canvas Retensioner, 16-ounce Spray is the perfect solution to most canvas tension problems. It instantly and safely tightens well-stretched canvases and paintings that have since slackened. Just brush or spray a small amount of the solution onto the back and canvas threads will safely swell and contract, causing the canvas to tighten. As the water evaporates, the fabric will lock into a contracted state, restoring canvas tension and leaving the surface flat and tight.