Paint a license plate by first using a paint remover to strip off the old paint, applying a primer designed for metals and then coloring the raised details using a small paint brush. Improve the paint's resistance to the elements by using all-weather enamel or epoxy-based paints.
If you plan to use the plate on an operational vehicle, contact your state's Department of Motor Vehicles. Many states allow using vintage plates on vintage automobiles, and they allow restorations that approximate the vintage plate's original look. However, most states do not allow modification of modern plates, and some states do not allow using vintage plates at all.
After stripping the old finish off of the plate, use a spray can or air compressor to spray both the primer and base coat onto the plate. This is quicker than using a brush, and it results in a more authentic, manufactured look.
The quickest way to apply color to the raised letters and numbers on the plate is by using a small, artist-grade paint brush and thinned enamel paints. However, even with multiple coats of very thin paint and a steady hand, some waviness and brush strokes are inevitable with this method. For a truly manufactured look, use a masking material such as frisket film, cutting out areas for the raised letters. Apply the color using a paint roller or sprayer, and then remove the mask. This method is more expensive and time-consuming, but it results in a more authentic finish.