Wash the door with a cleaner that contains a degreasing agent. Dry the door and sand it lightly with fine-grit sandpaper if the original paint or finish is glossy.
Paint a thin coat of crackle glaze onto the door, using a bristle brush or foam paint roller. Allow the glaze to dry for the amount of time specified on the container, typically between two and four hours depending on the brand.
Apply latex paint to the door, using a nap roller. Apply one coat and do not repaint over an area, as this can cause the crackle to pull away from the door surface. Paint in the direction of the wood grain.
Allow the paint to dry completely, usually overnight. Crackling occurs as the paint dries. Sand the edges of the door and the edges of any raised panels on the door, if applicable, to give a weathered, rustic look.
Paint the door with a thin coat of a clear water-based polyurethane sealer. The sealer protects the crackle so paint doesn't peel from the door. It also provides a gloss finish.