< GOLD
SILVER (STANDARD 925, STERLING, BRITANNIA)
Pure silver is almost as DUCTILE and MALLEABLE as pure gold which makes it ideal for COLD FORMING. The metal is also renowned for it’s high degree of THERMAL and ELECTRICAL CONDUCTIVITY (being significantly better in this respect than HIGH CONDUCTIVITY COPPER). Like golds, the silver alloys are best known for their use in jewellery production, decorative domestic designs and coinage. A few fine artists have also created limited works in silver alloys, the material being considered more suitable for sculpture making than the other noble metals. This is partly due to the relatively neutral colour of untreated silver, plus the ability of silver to take a variety of finishes, including a select number of chemical PATINATIONS. Silver stock is also markedly less expensive a material to purchase than other noble metals.
Silver is not used in it’s pure form for making design works instead, it is alloyed (primarily) with COPPER, which has a hardening influence on the metal. British standard or STERLING SILVER contains 7.5% copper, the US standard has a somewhat higher copper content, at about 10%. BRITTANIA SILVER is softer than either Sterling or US standard with a 4.16% copper content. High alloy silvers are usually preferred for casting purposes. Cast alloys also usually contain a small quantity of zinc, this functions as a deoxidising/scavenging agent in the charge, ultimately improving the quality of the cast – though the highest quality cast designs are often produced in controlled atmosphere casting chambers.
Wrought silver stock is available commercially from jewellery stockholders, though some artists (including Anthony Caro [1924-]), have made use of available ‘scrap’ silver (spent spinnings, cups, dishes and other similar shapes and sections), to make small scale sculptures. Silver alloys work harden and may require an annealing heat treatment to prevent the worked metal from stress cracking. FOIL (leaf) and ELECTROPLATING silver processes are also available for surface finishing copper alloy and other metal casts.
Joining sections formed in silver is usually done with a hard soldering technique and matching solder rod and flux, though heavier walled casts can be readily welded using the TIG process. Alternatively, mechanical fixings can be used, these include RIVETTED and PANNED DOWN or LAPPED self fixing joints.
Patination of cast, wrought or electroplated silver work is usually carried out by immersing the workpiece in a chemical bath, or else by direct application in the form of a paste or burial exposure. A range of colourings can be achieved through patination, these can vary from a dark matt finishes, through to electric ‘rainbow’ effects.
PLATINUM
Blue-white in colour, platinum is rarely used in the making of fine artworks, though it may be a constituent element in some (white) gold alloys. Wrought forms of this metal are available, though the hardness of the material in comparison to gold or silver makes it more difficult to manipulate and form into shapes. Leaf foil for the decorative finishing of works made in other metals is also available, as is an ELECTROLYTE for plating processes. The high cost of platinum metals means that for most artists and designers, the opportunity to explore uses for this metal is likely to be very limited.
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