Karat is a term used to indicate gold purity. Pure gold is 24 karat. The legal standard is to stamp gold jewelry with markings such as 10KT, 14KT and 18KT. The Karat stamp indicates the purity of the metal. The number preceding the KT marking indicates how many parts out of 24 are pure gold. The alloys mixed with gold are added to control durability, color and the cost of fine jewelry.

If you desire strong yellow color from your jewelry, 18 karat gold will give you the richest yellow appearance.  The disadvantage to 18kt is that it is not as durable or cost efficient as 14kt. Opinions vary about the most desirable karat from culture to culture. In America 14kt has become the most popular gold used in jewelry today due to its cost and durability. In western culture Jewelry made from 10kt has become synonymous with discount and lower end jewelry and is often brittle and difficult to repair.

This stems back to ancient times in the Mediterranean /Middle East, when a carat became used as a measure of the purity of gold alloys (see next Question 5). The purity of gold is now measured also in terms if fineness, i.e parts per thousand. Thus 18 carats is 18/24th of 1000 parts = 750 fineness.

The gold-containing ore has to be dug from the surface or blasted from the rock face underground. This is then hauled to the surface and milled to release the gold. The gold is then separated from the rock (gangue) by techniques such as flotation, smelted to a gold-rich doré and cast into bars. These are then refined to gold bars by the Miller chlorination process to a purity of 99.5%. If higher purity is needed or platinum group metal contaminants are present, this gold is further refined by the Wohlwill electrlytic process to 99.9% purity. Mine tailings containing low amounts of gold may be treated with cyanide to dissolve the gold and this is then extracted by the carbon in pulp technique before smelting and refining.