Enamel was first applied commercially to sheet iron and steel in Austria and Germany in about 1850. Industrialization increased as the purity of raw materials increased and costs decreased. The wet application process started with the discovery of the use of clay to suspend frit in water. Developments that followed during the twentieth century include enameling-grade steel, cleaned-only surface preparation, automation, and ongoing improvements in efficiency, performance, and quality.
Enamel in U.S. English, is a material made by fusing powdered glass to a substrate by firing, usually between 750 and 850 °C (1380 and 1560 °F). The powder melts, flows, and then hardens to a smooth, durable vitreous coating on metal, and also glass or ceramics, although the use of the term “enamel” is often restricted to work on metal, which is all that this article covers; enameled glass is also called “painted”. 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, but since the 19th century applied to many industrial uses and in everyday day consumer objects, especially cooking vessels.
Enamel may be transparent or opaque when fired; vitreous enamel can be applied to most metals. The great majority of modern industrial enamel is applied to steel in which the carbon is controlled to prevent reactions at the firing temperatures. Enamel can also be applied to copper, aluminium, stainless steel, cast iron or hot rolled steel, as well as gold and silver.
Vitreous enamel has many excellent properties: it is smooth, hard, chemically resistant, durable, scratch resistant (5-6 on the Mohs scale), long-lasting color fastness, easy-to-clean, and cannot burn. Enamel is glass, not paint, so it does not fade with UV light.
Its disadvantages are its tendency to crack or shatter when the substrate is stressed or bent, but modern enamels are chip and impact resistant because of good thickness control and thermal expansions well-match to the metal.
The key ingredient of vitreous enamel is a highly friable form of glass called frit. There are three main types of frit. First, ground coats contain smelted-in transition metal oxides such as cobalt, nickel, copper, manganese, and iron that facilitate adhesion to steel.
Second, clear and semi-opaque frits contain little coloring material for producing colors. Finally, titanium white cover coat frits are supersaturated with titanium dioxide which creates a bright white color during firing.
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