How can I smooth out creases in the canvas?

Creases in the canvas are a common problem, but they can be ironed out—literally. You can place heavy objects like books on top of the canvas, use a rolling pin, apply a heating pad, or carefully use an iron (on a low setting and with a protective cloth for stubborn wrinkles). For air bubbles, gentle use of a pen knife can be effective, and wrinkle-removing sprays are also available.