Amanda Sorensen, age 14, of Nashua, N.H., for her question:
HOW IS PORCELAIN ENAMEL MADE?
Porcelain enamel is a glass like substance that is used to decorate the surface of metal, glass or sometimes pottery. It is an artwork that has been popular since ancient times.
Porcelain enamel, sometimes simply called enamel, is made primarily of feldspar, quartz, silica, borax, lead and mineral oxides for coloring. After these materials are ground into fine particles, they are applied in various ways to the article to be enameled.
Articles being enameled are then fired at a temperature of about 1,500 degrees Fahrenheit. The heat melts the enamel and unites it with the surface of the article. The enamel must melt at a lower temperature than the object decorated, or the object may melt, too.
Because gold, silver and other metals, as well as glass, melt at higher temperatures than enamel, it is possible to protect them and decorate them with enamel. Depending on the formula, enamel is either transparent or opaque.
Glass, glaze and enamel are all related and the terms "glaze" and "enamel" are often used to mean the same thing. But glaze more often refers to a transparent coating for pottery or tiles.
Enamel may be applied in several different ways. For champleve enamel, a design is carved in metal and the depressions are filled with the enamel. The raised lines which remain form the outline of the design.
Cloisonne is made by bending thin strips of metal to form a design. The edges of the strips are fastened to the metal surface of the object and the spaces between the strips are filled with enamel.
The type of cloisonnel enamel without a metal foundation is called pique a juor.
Enameling was used by the ancient Egyptians, Greeks and Romans. It was also popular during the time of the Byzantine Empire and reached its greatest heights in the Middle Ages.
Enamels called surface face enamels are made by coating a metal surface with enamel on which a design is painted and then fired, making it permanent.
Bassetaille is an almost transparent enamel laid in thin coatings over a design that is engraved in metal.
Niello is a method of ornamenting gold and silver objects such as plates. A design is first engraved on the surface. Then a metallic compound made of silver, lead, copper and sulfur is put into the design and fired. The compound melts at a lower temperature than does the silver or gold. The surface is then smoothed and polished and the design is left in back.
Niello was used by the Egyptians, Greeks and Romans. Anglo Saxon jewelry in the early days also made much use of this technique. Many objects used for the Christian ritual in the Romanesque period were decorated with niello. It is still used today in India and Russia.
Limoges, France, became the best known center for the production of enameled articles.