GOLDEN FACTS
Gold is a chemical element denoted by the symbol Au, derived from the Latin word, Aurum. It is a soft and shiny yellow-coloured metal that is extremely malleable and ductile.
Malleability
One troy ounce of gold can be hammered into a sheet 31.105 square feet wide and one-thousandth of a millimetre thick, so thin as to allow light to pass through.
Ductility
One gram of gold can be drawn into 3.2 km long wire.
Purity
Pure gold does not rust, tarnish or corrode. The purity or fineness of gold is expressed in karats with 24 karat being the purest. Pure gold is too soft to be fashioned into jewellery, so it is alloyed with another metal - copper, silver, zinc, paladium, etc - to give it the necessary strength.
- 24k = 99.9% gold
- 22k = 91.6% gold + 8.4% alloy
- 18k = 75% gold + 25% alloy
- 14k = 58.3% gold + 21.6% alloy
- 12k = 50% gold + 50% alloy
In India, 22k gold having a purity of 91.6% is used in the manufacture of gold jewellery. However 18k gold has become increasingly popular.
Alloying Gold
Gold is yellow and copper is red. These are the only two pure-coloured metals. All other metals are whitish or greyish.
When gold of 99.9% purity is alloyed with copper, silver, zinc, aluminium, palladium, etc., different colours can be obtained. For example: 91.6 parts of pure gold with 8.4 parts of copper gives a pink or rose tone to the resultant alloy.
Coloured Gold
- Combining copper with gold results in a reddish colour.
- Adding silver or zinc to pure gold gives it a whitish colour.
- By adding a combination of copper, silver and palladium we get green gold.
- Controlled oxidation of 18k yellow gold with chromium or cobalt results in black gold.
Plating
Rhodium is used to plate gold jewellery to give it a bright and shiny look. A piece of jewellery in yellow gold can be made to look like white gold by rhodium-plating it. Rhodium-plating can wear off over time and with extended use. A piece of jewellery can be rhodium-plated again. Other metals can be plated with gold or silver too.
HALLMARKING
"Hallmarking is the accurate determination and official recording of the proportionate content of precious metal in gold." - The Bureau of Indian Standards (BIS)
Many countries require ornaments made in gold and silver to be assayed or tested for purity by an independent authority. This is for the protection of the consumer as well as to bring about standardisation of quality. The independent assayer stamps the jewellery with certain marks - the purity of the metal, manufacturer's mark, etc. This is called hallmarking.
In India, hallmarking is governed by the Bureau of Indian Standards.
Some of the advantages of hallmarked jewellery are:
- Uniformity in quality
- Government control
- Safety for the buyer
- Ease of export
A BIS-certified jeweller can register with any BIS approved hallmarking and assaying centre in India to get his jewellery hallmarked.
BIS monitors these certified jewellers at pre-defined periodic intervals.
Market surveillance involves BIS collecting jewellery from certified jewellers and testing them for conformity to standards.
A hallmark is a set of official marks used in many countries as a guarantee of purity or fineness of gold jewellery. In India, a hallmark consists of five components
- Fineness or purity of the gold - 23k, 22k, 21k, 18k, 14k, 9k, etc.
- Jeweller's mark
- Assay Centre's mark
- BIS mark
- Year of hallmarking, denoted by a letter. (A for the year 2000, B for 2001, C for 2002 ... N for 2014 and so on.)
