The process of gold leafing a wooden picture frame begins with a coat of shellac to seal the wood. Then many coats of gesso, usually about 12, are applied with a soft bristle brush. Each coat must be allowed to dry overnight and must be smoothed with fine sandpaper before the next coat is applied.
After all the coats of gesso have been applied, several coats of pigmented clays, called boles, are applied to the surface. The layers of clay provide additional cushioning for the gold leaf, and the pigment adds luster to the finished piece. Boles come in different colors, including black, yellow and red. The luster provided by a black bole base is popular in the United States, whereas yellow topped by red is more common in Europe. Rabbit-skin glue is added to the dry clay pigment to create a solution that is brushed on the piece in layers. The piece receives five or six coats of bole, and each must be allowed to dry overnight.
After the last coat of bole has dried, the piece is smoothed to a silky finish with 0000 steel wool. A gilding liqueur of denatured alcohol and distilled water is brushed on the frame, and a sheet of 24-karat gold leaf is carefully set on the piece. The gold leaf is gently dabbed in place with a soft-bristle brush and allowed to dry. After drying overnight, the gold leaf surface is reduced with an agate-tip burnisher.