What is Gold: Guide, Facts, Information, Resources, Knowledge. Learn All About Gold

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Gold guide gives gold information on

• Gold types
• Gold grades 
• Gold weights and measures
• Gold bars
• Gold alloy

Gold comes in many forms, both natural and manufactured. Gold can be classified into distinct types. Gold types are as follows:

• Lode gold - occurs in veins, grains or microscopic particles of metallic gold embedded in rock.
• Alluvial or Placer deposits - native gold is found as free flakes, grains or larger nuggets that have been eroded from rocks by water and other erosion mechanisms and deposited elsewhere.
• Bullion gold bar - are the traditional method for purchasing gold.
• Gold alloys - are produced for the jewellery (jewelry) industry.
• Rolled gold - is produced for the jewellery industry.
• Colloidal gold - is a suspension of nanometric-sized particles of gold in a fluid, usually water.
• Isotopic gold (Au, Aurum) - has one stable isotope, 197Au, and 18 radioisotope.
• Gold plate is either a dip of gold metal, electroplate or sprayed on.
• Gold leaf is an ultra-thin layer of pure gold.

For more information on all of these see Gold Type :: Gold Types by Humagaia.

There are a number of gold weights and measures utilised throughout the world, however the usual measures for international gold trade are avoirdupois (ounces, oz) and metric (grams, kilos and tonnes).

Where gold trade has continued for centuries there are other local gold measures such as:

• Tael (两 = chinese simp.; 兩 = chinese trad.; liǎng = pinyin) - China, Hong Kong and Taiwan. 1 tael = 40g approx.
• Tola (तोलक = Sanskrit; तोला = Hindi; تولا = Urdu; tolā, tolaka) - Indian subcontinent, Middle East and Singapore. 1 tola = 11.66g.
• Baht (บาท = Thai) - Thailand, 1 baht = 14.6g.
• Mesghal (پثسلاشم; Farsi) - Iran, 1 mesghal = 4.6g approx.
• Chi - (Vietnam) a Vietnamese unit of weight. 1 chi = 3.75g.
• Don - (Korean) South Korean measurement of gold weight.

A full description can be found in Gold Weights :: Gold Bar Weights by Humagaia.

Gold is graded in karat / carat. A karat (carat) is a measurement of the fineness of gold. The gold grade expresses the proportion of gold in a gold alloy or the quality of that gold alloy. Pure gold or fine gold is 24 karat / 24 carat (24k, 24 kt, 24 ct) gold (.999). 24k gold (999 fineness) is the grade of gold bullion.

The grades of gold reduce in karat fineness as more non-gold metal (alloy) is mixed with gold. Pure fine gold is very soft and malleable and does not lend itself well to gold objects that receive a lot of wear, as pure gold wears easily.

The various grades of gold for jewelry are as follows:

• 24k - this is pure gold, (999/1000, 99.999%, .999). This is the grade of gold GLD bullion.
• 22k - this grade of gold, (917/1000, 91.66%, .917) has been used to produce some coins and investment jewellery.
• 18k - most Continental European jewellery is made from this grade of gold (750/1000, 75%, .75).
• 15k - some older UK jewellery was made to this standard of gold (625/1000, 62.5%, .625)
• 14k - most North American jewelry is made with this grade of gold (583.3/1000, 58.33%, .5833).
• 12k - some older UK jewellery utilised this gold grade (500/1000, 50%, .5)
• 10k - this is the lower grade of Continental European gold (416.7/1000, 41.67%, .4167)
• 9k - most UK jewellery is made from the grade of gold (375/1000, 37.55, .375)
• 8k - this is the lowest grade of gold (333/1000, 33.33%, .333) acceptable for the manufacture of jewelry.

As we move down the table of grade of gold the metal alloy becomes harder and more resilient to wear and tear. Gold is a very soft metal and is easily rubbed away if it is in contact with gold jewellery of a lower carat.

A fuller information sheet about gold grades is available in Gold Grade :: Gold Grades by Humagaia.

An explanation of the various nomenclatures for gold grades is given in Table 1, below.

There are two main classification for gold bars:

• Cast - cast gold bars are made by pouring molten gold into a moulds of set dimensions. The manufacturer then adds assay marks, weight and purity details, either using a press or manually.
• Minted - minted gold bars are stamped out from a flat strip of gold, to the required dimensions, just as a coin is minted. The gold blanks created then pass through a minting press to apply assay marks, weight and purity details

depending on the manufacture method.

Further reading: Gold Bars by Humagaia

The purity of assayed gold bars is determined by expressing the gold content in terms of:

• parts per 100
• parts per 1,000
• parts per 10,000

according to the quality of the process creating the gold content of the gold bar.

No gold refining process is yet able to remove all impurities so the aim is to get to a purity of 100% but without actually achieving perfection. Many refineries are now able to express their end product in terms of parts per 10,000 and the norm is becoming 99.99% or 9,999 parts gold to10,000 parts of product.

This is becoming the norm but "standard" gold bars do vary according to the country where they are produced:

• Dubai - 99.9% or 999 parts gold per 1,000 parts product.
• Iran - 99.5% or 995 parts gold per 1,000 parts product.
• Hong Kong - 99% or 99 parts gold per 100 parts product.
• Thailand - 96.5% or 96.5 parts gold per 100 parts product.

Good London Delivery (GLD) bars, held by central banks, which are 12.5kg (400 oz) weight, are normally at least 99.5%.pure or 995 parts gold per 1,000 parts product. The trend though is towards a higher purity of 99.99% or 9,999 parts gold to10,000 parts of product.

Pure gold is soft and very malleable.

The carat gold alloys range in gold content from 8 to 22 carats

Metallurgists must take into consideration how various precious metals react to one another. Formulating gold alloys is very challenging. Too much of one precious metal can cause the combination to become fragile, hard and will prove difficult to design jewellery. Another combination of precious metal may cause the alloy to become too soft for jewellery fabrication.

All gold alloy have different mechanical properties such as strength, hardness and malleability (ductility) and some alloys can be heat treated to maximise strength and hardness.

There are hundreds of gold alloy and gold mixtures possible. Generally the addition of silver will colour gold green. The addition of copper will colour it red. A mix of about 50wt%:50wt% copper : silver will give a range of yellow gold alloys. Those that you are accustomed to seeing at the jewellery store..

A small amount (0.2wt%) of zinc will harden the alloy.

There are some more unusual alloys of gold. Where gold is mixed with silver, Iron, cadmium or aluminium one can obtain green, blue and purple gold compounds.

Another technique, which involves the formation of a coloured oxide layer on the alloy during heat treatment in air is surface oxidation.

For further reading see: Gold Alloy by Humagaia.

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