Archives October 16, 2002 admin
Gold: Alloys And Colors
|BLUE GOLD 18K||75% GOLD
|YELLOW GOLD 14K||58% GOLD
|YELLOW GOLD 18K||75% GOLD
|YELLOW GOLD 22K||92% GOLD
|GREEN GOLD 18K||75% GOLD
|RED GOLD 18K||75% GOLD
|STERLING SILVER||92.5% SILVER
|WHITE GOLD-1||90% GOLD
|WHITE GOLD-2||75-85% GOLD
|WHITE GOLD – 14Kt A||58.3% GOLD
|WHITE GOLD – 14Kt B||59% GOLD
|WHITE GOLD – 18K||75% GOLD
(FROM: Engineering Alloys, Fifth Edition, Edition by Woldman & Gibbons)
Pure metals have very precise melting points – silver 961C, gold 1063C, platinum 1769C. Alloys however, being mixtures melt over a range of temperature. 18kt yellow gold melts typically at 895-930C.
Metals have a crystalline structure. When a metal is strained and distorted mechanically, the crystals become stressed and the metal hardens. To relieve this stress, and “relax” the structure, they must be heated to a temperature somewhat below the melting point. This is called annealing. Gold alloys must be cooled slowly after annealing.
Pure gold is very soft (Mohs hardness 2.5-3). It is commonly wrongly belived that the purer the the alloy of gold, the softer it is. In fact, there are several different types of hardness.
Ductility refers to the flow characteristics of a metal under pressure, undergoing plastic deformation in stretching, bending etc. Maleability is how the metal deforms uncer impact from a hammer or punch.
After annealing, gold is generally quite ductile (soft). Fine golds are softer than carat golds.
Deforming metals by pressure or impact causes them to harden, at differing rates dependent on the alloy. As it hardens, it becomes less deformable, and more brittle.
Most alloys containing copper will age-harden. This may be apparent over months to years.
The wear resistance is related to its surface hardness and age as well as to the actual metal. For eg, the annealed hardness of 9 & 18 kt golds are similar. 18, 14, 9 kt golds are considerably harder than 22 or 24 kt golds. Annealing softens them, and working (bending, twisting) tends to work harden metals (this explains why forged steel is much stronger than cast steel for the same alloy content).
These are most commonly caused by allergies to nickel; if so, w/gold which contains nickel, should be avoided. In addition, tight fitting, poorly ventilated bracelets worn in humid climates are invitations to fungal infections.
SOME OTHER TRIVIA:
121,000 tons of gold have been mined so far (only 15% of this is missing). 43% of known gold lies in Central Banks. Over 80% of gold produced in a year goes to jewellery and (less) watches.
I hope that this article has provided a cure for insomniacs, and some salient information for other gold diggers of minutiae.
I have to go now, my wife is on my back – she can’t sleep while I’m pecking on the computer. Goodnight all!