COPPER & COPPER ALLOYS
Archeological evidence from excavations at Catal Huyuk in Southern Anatolia (now part of Turkey), suggests that copper was being refined by man as early as 7000 BC [ref]. The lengthy availability of workable copper materials means that many surviving artifacts of historical and technical interest (not to mention artistic merit), have been formed in this metal and it's subsiduary alloys.
Today, casting in one or another of the copper alloys accounts for the greater part of any art foundry’s output; indeed some founders will only cast client work in a single preferred copper alloy. From the founder’s point of view copper alloys are generally forgiving to cast and straightforward to work with; the molten charge flows well into all types of refractory mould, with casts formed in the more common alloys are relatively easy to weld, chase and machine - soft enough to work, strong enough to form sound long-lasting structures. The vast majority of copper alloys also allow for a fine finish to be worked onto the cast’s surface, usually this is in the form of a high mirror polish or chemical patina.
COPPER (HCC & C SERIES)
Copper is available in a highly purified form (>99.90% Cu), as both as cast and wrought material. Due to it’s low resistance to electricity and heat, the primary use of this metal is as a conductor, hence the designation HCC or HIGH CONDUCTIVITY COPPER (US Grade ‘A’). Few, if any cast artworks are produced in this highly refined metal, principally due to it’s relative expense and the difficulties encountered in casting and working a near elemental material. Where a high copper finish is required on a cast work, it may be more practical to request a more common casting alloy such as a GUNMETAL, then later deposit a fine copper electroplate over the design. Alternatively, copper GILDING leaf is readily available in both loose and transfer foils.
Most 'fine' copper sculptures and designs are produced from wrought sheets and other preformed sections. Stock material of this sort is readily available from a good non-ferrous metal stockholder in a variety of hardnesses. Wrought sheet can be profile cut by a PLASMA or CNC WATER-JET process (not LASER). Thin gauge soft copper sheet is well known for it’s suitability for creating raised REPOUSSÉ works by hammering. Unless a specifically ‘high copper’ finish is called for, phosphor copper (PHOSPHOR BRONZE), is generally preferred for use over copper for direct sculpture fabrication; silicon bronze (Cusilmn pronouced 'Quzilmen'), is another option.
Copper casts and fabrications are typically joined and repaired using a S, or OXY-GAS process (welding, soldering and brazing). The alloy version BS 2874 C106 (Cu-DHP) is deoxidised and therefore considered the most suitable grade for TIG welding (using a C21 type filler rod). Owing to the material’s excellent conductivity, either high current settings [arc] or large bore heating nozzles [gas] are necessary to achieve the formation of a good weld pool. The use of HELIUM as a gas shield instead of ARGON when TIG welding copper can lower the current setting needed to form a good weld pool.
Thin walled COPPER sections (such as plumbing tube), is normally soft soldered using a LPG or butane fuelled torch with a lead (or lead replacement) solder and flux protection. Hard silver soldering is generally preferred for joining light gauge decorative and jewellery works in copper. Copper sheet can also be rivetted, or secured with a self fixing ‘panned over’ joint. Copper will accept a wide variety of chemical patinations and other specialist finishes, similar to those commonly applied to the metal's derivative casting alloys (GUNMETALS and bronzes etc). If stock copper material for patination is supplied pre-polished, it is often first lightly keyed (SHOT BLASTED) to improve the adherence of the patina deposit – though care must be taken not to stretch the metal by using too high a blast pressure. The metal polishes to a high lustre/mirror finish and offers good resistance to corrosive attack.
download pdf: Copper Family Tree (49kb)
A copper sheet marked out for
pressing into a cone form.
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