Silver, which occurs naturally, has been one of the noble metals since antiquity, second only to gold in aesthetic and commercial value. Pure silver is difficult to work with, so, for the production of silver jewelry, it is generally alloyed with other metals, particularly copper. The proportions of silver to copper in what is typically called Sterling silver is 925 parts of silver and 75 parts of copper. For this reason on the continent this type of silver is often referred to as “925 silver”. The better silver/copper alloys are made with oxygen-free copper in order to avoid oxidation, which gives the finished products a dull and opaque appearance. Alloys made with such oxygen-free copper are therefore whiter and brighter.
The first step in achieving a silver alloy suitable to being made into jewelry is thus the fusion of the silver and the copper. This is generally subdivided into two distinct steps: the pre-fusion, which utilizes induction or microwave ovens, and the fusion itself, which utilizes horizontal casting ovens. In the pre-fusion phase the two metals are placed in a graphite crucible and quickly liquefied by powerful magnetic fields. The temperature reached in the crucible is about 980 deg Celsius.
The second step involves the horizontal casting oven. The molten metal is poured into a thermally isolated chamber in which the temperature is maintained at a constant 980 deg Celsius. It is then made to flow through a cooling circuit and it is extruded as a solid in the form of a sheet about 7 mm in thickness.
The coarse sheet thus obtained is now thinned and elongated by passing it between rotating rollers, much like dough through a pasta machine. The lamina thereby obtained typically has a thickness of 1 mm, still too thick for optimal shaping. It is therefore pressed between a second pair of finer rollers, in a process called finishing. The resultant fine lamina has a thickness of about 0.25 to 0.30 mm, ideally suited to be worked by hand in the subsequent steps. The fine lamina is now rolled up into a bundle and cut longitudinally to yield silver ribbons of the desired size.
One complication is that, during the process of lamination, the alloy becomes brittle and susceptible to breakage. To obviate this problem in later work the metal if recooked, i.e., brought to a high temperature and then allowed to cool. This is done in a tunnel oven, which is a thermostatically controlled chamber in which an oxygen-free atmosphere has been introduced. The silver lamina or ribbon is pulled through the tunnel oven while the temperature is carefully controlled.
The silver ribbons are now ready to be turned into jewelry to add allure to a beautiful woman or into art objects to add beauty and elegance to a fine home.
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