Vitreous enamel

Vitreous enamel, also known as porcelain enamel, is a material made by fusing powdered glass to a substrate by firing, usually between 750 and 850 degrees Celsius. The powder melts, flows, and then hardens to a smooth, durable vitreous coating on metal, glass, or ceramic. The term "enamel" is most often restricted to work on metal, which is the subject of this article. The fired enameled ware is a fully laminated composite of glass and metal. Enameling is an old and widely adopted technology, for most of its history mainly used in jewelry and decorative art. Since the 19th century, enamels have also been applied to many consumer objects, such as some cooking vessels, steel bathtubs, and stone countertops. It has also been used on some appliances, such as dishwashers, laundry machines, and refrigerators, and on marker boards and signage.

The key ingredient of vitreous enamel is a highly friable form of glass called frit. Frit is typically an alkali borosilicate chemical with a coefficient of thermal expansion and a melting point compatible with the metal to which it is to be applied. The frit is finely ground, mixed with a fluxing agent, and sometimes a colorant, then applied to the metal surface. The coated metal is then fired in a kiln, allowing the frit to melt and fuse to the metal. The process can be repeated to build up layers of enamel, which can then be etched, carved, or otherwise manipulated to create a design. The final product is a smooth, hard, and glossy surface that is resistant to corrosion and wear.

Enameling has a long history, dating back to the ancient Egyptians, who used it to decorate jewelry and other small objects. It was also popular in ancient Greece and Rome, and throughout the Middle Ages in Europe. In the 18th and 19th centuries, enameling became a popular technique for decorating watches, snuff boxes, and other small items. Today, vitreous enamel is used in a wide range of applications, from jewelry and art to industrial and architectural design. Notable artists who have worked with enamel include René Lalique, Fabergé, and Alexander Calder.