< METAL SPRAYING & BRONZING
ENAMELLING
Enamelling sculpture involves the application of a VITREOUS medium (BOROSILICATE), which is ground and coloured with the addition of METAL OXIDES. The cast is first cleaned, after which the liquid enamel body can be applied and air dried before oven baking. This procedure may be repeated on a number of occasions to achieve the desired quality and effect of finish.
Care should be taken in selecting a suitable alloy for cast when enamelling, as undesirable reactions can occur between the vitreous medium and the compounds present in the cast alloy. As a rule, few works formed in copper alloys are suited to an enamelling process, though notable exceptions include 90/10 phosphor bronzes and gilding metal (the BRASS alloy CZ101 [ISO CuZn10]). Alternatively, grey cast iron (to BS 1492:1961), low silicon/low copper bearing cast aluminium (to BS 1490:1988), and VE (vitreous enamel) quality wrought steel (ie. sheet material with a very low carbon content to BS 1449[1]) are suitable materials for enamel finishes.
Heating a design formed in a low melting point alloy to the elevated temperatures required for oven baking (750-900°C) may cause damage or distortion. Always remember that ‘blanked off’ hollow castings could potentially explode in the oven, unless a relief hole is first drilled through the cast’s wall thickness to equalise air pressure. Similarly, any air trapped within sub-surface holes resulting from cast inclusions or weld porosity, is also likely to expand and damage the enamel finish (see SUPPLEMENT). Sharp breaks of form should be avoided as enamel can easily crack off angular edges, and the cast’s wall thickness should be made as even as possible to promote uniform heating.
Enamelling bronze works for decorative purposes was especially popular during the 19th century. In particular, soldered metal strip would be applied to the cast surfaces, defining areas which were then filled with applied layers of enamel. Known as CLOISONNÉ, this finishing technique is rarely practiced today, though an excellent enamel on copper example is held in the collections at the South Australian Art Gallery (Adelaide), titled ‘Human Human Coloisnné Bust 3’ 2001, by the artst Ah Xiau (1960).
ANTIQUE PAINT FINISHES >
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