all about Gold
Gold is a dense, valuable, bright yellow and lustrous shining metallic chemical element. It is found in nature in quartz veins and secondary alluvial deposits (transported by water). Although it is rare, it is widely distributed throughout the world, with two thirds of global production coming from South Africa.
Experts estimate that gold mined in the past 6000 years would exceed 100,000 metric tonnes and its biggest use is in jewellery. That translates to a lot of individual pieces, especially when you consider that it takes an average of three tonnes of rock to recover just one ounce of gold.
The aim of the refining process us to remove all impurities, leaving pure gold.
The origin of the gold determines the method of initial refining to separate the precious metal from the earth. The source of the gold (quartz veins or alluvial deposits) determines its method of extraction and processing.
Gold found in quartz veins must be brought to the surface and crushed into a fine powder. The gold is then dissolved in cyanide and the solution is then filtered to remove any rock particles. Zinc dust is then added to separate the cyanide from the gold. Gold then emerges as an impure powder which is then melted into gold ingots.
Gold sourced from an alluvial deposit refers to gold that has been transported by water and deposited in river beds. Gravel from riverbeds is separated by screening out smaller stones. Gravel that is less than 10mm in size containing gold is then washed over a ridged table. These ridges trap the gold which is heavier than the gravel. These gold particles are then collected and melted into ingots.
Gold from both origins then goes to a refinery for further processing to remove impurities (silver, copper, lead).
The gold is re-melted, splattered, then dissolved in a mixture of hydrochloric and nitric acids. This solution is then filtered to remove impurities, and sulphur dioxide added to separate the acid from the gold. Emerging from this is gold in pure powder form which is then melted into granules (these resemble rice bubbles!).
The granules are pure gold (also known as fine gold or 24ct gold). Pure gold granules are the basis of all gold alloys.
ALLOYING AND THE FINENESS OF GOLD
While gold is refined to pure, the gold used in the manufacture of jewellery is more commonly an alloy. An alloy occurs when two or more metals are mixed, usually to obtain different working qualitites, or vary the colour. The amount of pure gold in the alloy, and what it is alloyed with, will determine the caratage and the colour of the final product.
As 24ct is considered too soft for jewellery, gold is alloyed with other metals to achieve the required hardness and malleability.
The most frequently used metals in gold alloys include silver, zinc, copper, palladium and platinum.
Allergic reactions to precious metals are most uncommon; it is more likely to be a base metal in an alloy that has caused a problem. It is also possible that one 10ct gold alloy may result in an allergic reaction while another does not. There are fewer allergic reactions to white golds as they contain fewer impurities.