Types of Porcelain Enamels

Porcelain enamels for sheet steel and cast iron are classified as either ground-coat or cover-coat enamels. Ground-coat enamels contain metallic oxides, such as cobalt oxide and/or nickel oxide, that promote adherence of the glass/enamel to the metal substrate. Cover-coat enamels are applied over fired ground coats to improve the appearance and properties of the coating. Also, cover-coat enamels may be applied over unfired ground coats, with both coats being fired at the same time (i.e., two-coat/one-fire systems). Cover coats may also be applied directly to properly prepared decarburized steel substrates. The color of ground coats is limited to various shades of blue, black, brown, and gray. Cover coats, which may be clear, semiopaque, or opaque, may be pigmented to take on a great variety of colors. Colors may also be smelted into the basic coating material. Opaque cover coats are usually white.

Porcelain enamels for aluminum are normally one-coat systems. They are applied only by spraying. When two coats are desired, the first coat can be any color. Frits for porcelain enamels for aluminum are usually transparent and may be colored and opacified with inorganic pigments to produce the desired appearance.

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