1) porcelain enamel powder often is applied as a paste, and may be transparent or opaque when fired; vitreous porcelain enamel powder can be applied to most metals. It has many excellent properties: it is smooth, hard, chemically resistant, durable, can assume brilliant, long-lasting colors, and cannot burn. Its disadvantages are its tendency to crack or shatter when the substrate is stressed or bent. Its durability has found it many functional applications: early 20th century advertising signs, interior oven walls, cooking pots, exterior walls of kitchen appliances, cast iron bathtubs, farm storage silos, and processing equipment such as chemical reactors and pharmaceutical chemical process tanks. Commercial structures such as gas stations, bus stations and even Lustron Houses had walls, ceilings and structural elements made of porcelain enamel powderl steel.
2) Color in porcelain enamel powder is obtained by the addition of various minerals, often metal oxides cobalt, praseodymium, iron, or neodymium. The last creates delicate shades ranging from pure violet through wine-red and warm gray. Porcelain enamel powder can be either transparent, opaque or opalescent (translucent), which is a variety that gains a milky opacity the longer it is fired. Different porcelain enamel powder colors cannot be mixed to make a new color, in the manner of paint. This produces tiny specks of both colors; although the eye can be tricked by grinding colors together to an extremely fine, flour-like, powder.
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