Crackle medium allows you to create the look of aged, weathered paint without waiting years to achieve it -- the effect starts as soon as you brush on the top coat of paint. While using a crackle medium is a fairly straightforward process, timing is everything when it comes to creating the crackling -- wait too long and the paint doesn't crack at all, so you'll have to start again with a fresh layer of crackle medium.
A crackle finish works on just about any type of item that can be painted with acrylic or latex paint, but it looks the most realistic on painted pieces that would normally weather over time -- such as wood furniture, crates, painted craft projects and even painted wall art. Crackle medium also works over varnish, but keep in mind it's the base finish that shows through the cracks when you're done. Prime, then paint a sanded wood project with a base paint color if it's not painted in a desired shade already; allow the paint to dry completely before using crackle medium. Select a base paint color different from the top color -- the more different the two shades, the more obvious the cracks on the finished product.
Applying Crackle Medium
Brush crackle medium over the entire piece, or only on specific areas if you want to crack certain features, such as drawer fronts or a tabletop. Apply the medium with a foam brush, and make sure each stroke covers the entire length or width of the project area, otherwise it may not crackle properly. The crackle medium is ready for painting when it's slightly tacky but not dry, typically one to four hours. Read the crackle medium package, as drying times vary greatly from one product to the next -- some brands use a different formula that requires the crackle medium to be dry.
Applying the Paint
Brush your chosen latex or acrylic top-coat color over the tacky crackle medium. Select a flat paint for best results; glossy or metallic paints may not crackle, although they will work for the base paint color. The thicker the top coat of paint, the larger the cracks, in most cases. Cracks should form within moments if you've applied the paint at the right time. Allow the paint to dry completely for all the cracks to form on their own. A sealer is optional but not necessary; it may make the project look too shiny and new, detracting from the weathered look.
Homemade Crackle Medium
Instead of purchasing a dedicated crackle medium, use a basic school glue or wood glue instead. Glue works just like crackle medium for creating a crackled finish, although it dries much more quickly. The glue may be ready to paint in 10 minutes or so -- keep the paint and paintbrush handy, touching the glue every five minutes to make sure you're ready when the glue is.