Duncan Ceramic Spray Sealers porcelain 12 oz. Ceramic Spray Sealers are final spray coatings that produce smooth, hard surfaces and are used to brighten colors and protect the finishes of objects decorated with nonfired color products. Porcelain Spray produces the look and feel of fine porcelain bisque when applied over a fired glaze or Prep-Coat. It works especially well as a final finish over dry-brushed items and can be used under, over and between nonfired colors.