What is porcelain enamel?
In general terms, vitreous enamel, porcelain enamel, copper enamel and jewelry enamel all refer to the same thing. Porcelain enamel is a glassy compound applied to and bonded by heat (fusion) to a metal surface; to a copper surface at 1450 degrees F., and to a glass surface at 1100 degrees F. to 1500 degrees F.
The most common glass is a fusion of silica, soda, lime, and a small amount of borax. Though normally transparent, various amounts of opacity can be produced by adding or growing crystals within the glass structure. A wide range of colors are produced by incorporating certain elements, mostly transition metals.
The physical properties of glass can be controlled to permit bonding to most metals, for example, gold, platinum, silver, copper, steel, cast iron and titanium.
The word ‘porcelain enamel’ refers to the glass material as well as to the finished product.
How is it done?
Porcelain enamel (glass) is crushed to a powder somewhat finer than granulated sugar and somewhat coarser than flour. This powder is applied, by one of several methods, to the metal or glass surface. Next the article is heated to 1100 to 1500 degrees F., either in a pre-heated furnace, a hand held torch, or for porcelain enamels fused to glass, in a kiln. For metal, in a preheated furnace the article may be fired from 1 to 5 minutes, depending on size or technique. The article is removed and allowed to cool to room temperature. Subsequent coats, normally different colors are applied. Sometimes many firings are required to bring about the desired results. For fusing porcelain enamels to glass, the article is placed into a room temperature kiln and the heat is brought up according to the appropriate firing schedule to the maturation temperature, then brought down to an annealing temperature and held there for a period of time to relieve stresses in the glass, then brought back down to room temperature before removing the article.