a network on glass,') where enamelled metal is suspended in glass. The technique was briefly popular in seventeenth-century France and was re-discovered by Margret Craver in 1953. Craver spent 13 years re-creating the technique. Other types: Enamelled glass, in which a glass surface is enamelled, and fired to fuse the glasses. Stenciling, where a stencil is placed over the work and the powdered enamel is sifted over the top. The stencil is removed before firing, the enamel staying in a pattern, slightly raised. Sgraffito, where an unfired layer of enamel is applied over a previously fired layer of enamel of a contrasting colour, and then partly removed with a tool to create the design. Serigraph, where a silkscreen is used with 60–70in grade mesh. Surrey enamel, a 17th-century type for brass objects such as candlesticks; effectively champlevé. Counter-enamelling, not strictly a technique, but a necessary step in many techniques, especially painted enamel on thin plaques; introduced in 15th-century Europe. Enamel is applied to the back of a piece as well – sandwiching the metal – to equalize the rates of expansion under heat, and so create less tension on the glass so it does not crack. Safed chalwan, where jewels are set in white enamel See also Japanese shipōyaki techniques. Industrial enamel application On sheet steel, a ground coat layer is applied to create adhesion. The only surface preparation required for modern ground coats is degreasing of the steel with a mildly alkaline solution. White and coloured second "cover" coats of enamel are applied over the fired ground coat. For electrostatic enamels, the coloured enamel powder can be applied directly over a thin unfired ground coat "base coat" layer that is co-fired with the cover coat in a very efficient two-coat/one-fire process. The frit in the ground coat contains smelted-in cobalt and/or nickel oxide as well as other transition metal oxides to catalyse the enamel-steel bonding reactions. During firing of the enamel at between , iron oxide scale first forms on the steel. The molten enamel dissolves the iron oxide and precipitates cobalt and nickel. The iron acts as the anode in an electrogalvanic reaction in which the iron is again oxidised, dissolved by the glass, and oxidised again with the available cobalt and nickel limiting the reaction. Finally, the surface becomes roughened with the glass anchored into the holes. Building cladding Enamel coatings applied to steel panels offer protection