May 4, 2009

Vitreous Enamel

Vitreous enamel coating on metal are films of glass, opacified with inorganic pigments. Such coatings have the excellent chemical resistance and inertness of glass, together with both hardness and gloss. This makes them very suitable for coating on metals to resist the weather, water, chemical solutions, foodstuffs and beverages, as well as heat.

Vitreous enamel coatings have been used since ancient times on a craft scale for jewellery and decorative table and toilet wares, because of the attractive effects, which could be obtained. In these cases they were usually applied to silver or copper. They have also been used on other non-ferrous metals for instrument parts, such as watch dials. Enamels steel pots and pans, kettles, basins and jigs were formerly very common, but have now largely been replaced by aluminum, stainless steel and plastics.

Vitreous enamels is still much used for baths and other sanitary ware, and for chemical and food handling plant. Another considerable use of enamelled steel is in the construction of signs where the significant lettering or symbolism stands out from the back ground by the use of a different color.

Whilst the surface of vitreous enamel withstands exposure to the weather of to water for many years without appreciable change, its suffers from the inherent brittleness of glass. Thus if the vetreous enamelled sheet is bent, dented or flexed, the enamel cracks, and may even spall off. In such cases the exposed steel rusts; this disfugures the coating over adjecent areas, but more seriously, it may spread laterally under the adjecent enamel, which becomes prised off. Paint film are much less brittle, but formerly had poorer weather resistance. As the quality of paints has improved in recent years they have tended to supplant vitreous enamed. It may in fact sometimes be quite difficult to differentiate between a well-applied stoved paint finish and a fired vitreous enamed. However only vitreous enamel will withstand elevated temperatures without change, it is therefore much used for stove parts, cooking appliances and similar articles.

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