REAL JEWELLERY MANUFACTURING UNIT

Gold has a characteristic pleasing colour but it assumes various colours, e.g: deep violet, ruby and purple, when reduced to a finely divided state by volatilization or colloid formation. It is the most extensible of all metals and can be reduced by hammering to a thickness of 0.00008. Impurities specially tellurium, bismuth, and lead reduce its malleability and ductility pure gold melts at 1063oC. Gold-copper alloys are harder more fusible and less malleable and ductile than pure gold. They have higher tensile strengths. The densities of these binary alloys are lower while those of triple alloys of gold, silver, and copper are higher. Gold silver alloys are soft, malleable, and ductile and their properties are intermediate between those of gold and silver. Gold iron alloys are hard but malleable & ductile. Gold and mercury form amalgams at ordinary temperatures. Mercury dissoves 0.11% of gold at 0oC and 0.126% at 100oC. Gold absorbs mercury forming a silver-white solid containing about 40% gold. On heating the mercury volatilizes leaving the gold residue. In addition to its use as a medium of international exchange and as a fiduciary to paper currency, about 5-10% of the world annual production is consumed in the useful arts. Its high specific gravity, resplendent lustre, pleasing colour, and non tarnishing quality have made it the most coveted metal for jewellery and comage since ancient times. The chief uses of gold are in comage, jewellery, dental alloys gold coating of base metals, and scientific instruments. The properties of gold which are valued in trade and industry are its pleasing colour and resistance to corrosion; malleability and ductility; low specific heat and latent heat of fusion; high electrical conductivity and reflective power; & therepeutic effects of some of its salts. Alloys of gold and iron are used in France for making jewellery under the name of gris; the iron content varies between 15 and 20%. Aluminium forms a number of alloys with gold. One of them AuAl2(22%Al) has a remarkable purple colour. The so called aluminium-gold is an alloy of copper with about 25% aluminum. It resembles gold in colour and it also slightly attached by nitric acid. Many recipes have been formulated for soldering gold. Many of them contain a considerable proportion of zinc with copper, silver, and gold. In the prescence of copper, zinc does not cause brittleness, though the alloy formed is extremely hard and difficult to roll. Cadmium has been substituted for zinc in soldering alloys. The solders lose Zinc or cadmium by volatilization when heated and gradually become less fusible.