Gold – the metal of Kings and Gods! Gold is the only naturally yellow metal and has extraordinary physical properties.
- It is a highly reflective metal (second only to silver). That means when it is polished it reflects back most of the light which strikes it, so it looks very bright and beautiful.
- It is a noble metal – meaning it is virtually incorruptible. Copper tarnishes, iron and steel rust away but time and the elements cannot touch gold. After thousands of years it is just the same eg. Tutankhamen treasures. Oxygen and acids will attack most metals – but not gold. Pure gold is only attacked and dissolved if placed in a boiling mixture of nitric and hydrochloric acid, otherwise known as boiling Aqua Regia
- It is the most malleable of all metals meaning it is workable and responsive to craftmens tools. One ounce of gold can be hammered out to produce 100 square feet of fine gold foil.
- It is the most ductile of metals meaning it can be drawn down to produce very fine wires to be used in making jewellery. One ounce of gold can be turned into 50 miles of wire.
- It is quite a soft metal, in it’s pure state, which also makes it good to work but does mean it does not withstand wear too well.
- It is a very heavy metal. This means for its size it weighs more than most other metals eg. The specific gravity for gold is 19.32 compared to only 11.35 for lead.
- It has a relatively low melthing point compared to other metals.
Gold is rare in that it is difficult and costly to extract from the earth and is wanted for industrial uses as well as for jewellery manufacture. For many centuries gold has been a measure of the wealth of nations and still underpins the economy of all the industrial nations of the world.
Technical information: Pure gold is measured as 24 carat or parts.
A number of elements are added to gold to change its properties – this is known as gold alloy and depending on the amount of other elements the legal standards of gold currently used in the UK are as follows:
- 22 carat gold which contains 22 parts of gold and almost two parts of other metals,
- 18 carat gold which contains 18 parts of metal and approximately 6 parts of other metals,
- 14 carat gold which contains 14 parts of gold and approximately 10 parts of other metals,
- 9 carat gold which contains 9 parts of gold and approximately 15 parts of other metals.
- 18, 14 and 9 carat are qualities that can be produced in white gold also.
- Commonly used elements in gold alloy are: Silver, copper, zinc, palladium, nickel and silicon.
- Units of weight are either Troy Ounces (old, traditional) or Grams (modern, metric)
- Some countries produce limited quantities of gold coins such as Sovereign, Krugerrand, Canadian Dollar, Mexican Peso and US Dollar and are often used in rings and pendants.
- Coloured Gold: Below 22 carat it is possible to make gold alloys of various shades of colour depending on the other metals which are mixed with the gold.
- White gold uses nickel, palladium or zinc in the alloy composition to “bleach” the natural colour of the gold content. It was discovered how to make white gold in 1914 – 1918, during the first World War, when the supplies of platinum ran short. Almost all white gold articles manufactured today are given a thin surface plating of Rhodium – this will sometimes need re-plating as it wears off and the grey, yellow tinged colour of the raw white gold shows through.
- Red gold uses a high proportion of copper to produce a reddish coppery colour gold.
The British system of hallmarking precious metals is one of the oldest forms of consumer protection and can only be legally described as such if they bear the appropriate hallmarks by one of the official Assay Offices (Government-authorized bodies). It is the responsibility of the Assay Offices to test articles to make sure that they contain the minimum required proportion of precious metal.
Therefore a hallmark is a series of little marks or symbols stamped or lasered onto articles of jewellery to confirm the standard of gold, platinum or silver contained in the item. A full hallmark will contain the Sponsor Mark (manufacturer’s mark which has to be registered with the Assay Office), the Standard Mark (which shows the precious metal content of the alloy), the Assay Office Mark (also known as the “town mark”) and the Date Letter (shows the year of hallmarking). The most recent Hallmarking Act came into force on 1st January 1975 and since then only articles which are hallmarked can legally be described by retailers in the course of trade or business as gold, platinum or silver. Items can still be sold but it is the description which is controlled. Any article which weighs 1 gram or more should be hallmarked under this Hallmarking Act.
From 1975 the Standard Mark shows the content of precious metal as parts of 1000. Therefore 22 carat is 916, 18 carat is 750, 14 carat is 585, 9 carat is 375, silver is 925 and platinum is 950.
In Victorian times there were two further caratages in popular use – 12 and 15 carat gold, sometimes marked as .5 and .625 respectively. The terms carat or caratage refers only to gold – they are not used to describe silver or platinum.
Silver has a long history of use for making jewellery and a long historical use for coinage. It has remarkable physical properties
- It is the highest reflective metal of all. That means when it is polished it reflects back 95% of the light which strikes it, so it looks very bright and beautiful.
- It is a noble metal – meaning it is virtually incorruptible. However silver does tarnish because it is strongly affected by sulphur which is present in the air
- Like gold silver is also malleable and ductile meaning it is excellent to work with and can be easily shaped
- It has a greater tensile strength than gold so can be easily bent, stretched and shaped without the tendency to crack
- It is a comparatively light metal with a specific gravity of only 10.49 (compared to 19.32 for fine gold)
- It is a soft metal (although a little harder than gold). This is a disadvantage as it scratches easily but because it is soft it can be polished out again.
Just as gold is not used in its pure state for jewellery, so silver is also mixed with other metals – chiefly copper. That makes the alloy rather harder and stronger than pure silver.
There are two standards of silver alloy that can be legally described as silver in the UK. One is Sterling Silver (or Hallmarked Silver) which is 925 parts of silver to every 1000 parts of alloy. This is the most usual standard found in the UK. From 1975 the traditional mark for England is the Lion Passant and the Edinburgh Assay Office uses a lion rampant. Any article which weighs 7 grams or more should be hallmarked under the requirement of the Hallmarking Act.
The other is Brittania silver which contains 958.4 parts of pure silver in every 1000 parts of metal alloy. This is not a commonly used alloy. Some European silver is of lower standard than the UK. 800, 830, or 850 parts of 1000 may be used – these cannot be legally described as silver by British standards. The same units of weight are used as for gold
Platinum is a naturally white metal that tends to be used for higher quality jewellery, settings and in combination with 18 carat yellow or white gold. It is one member of a family of six metals all with different names. Only two other members have an interest for the jeweller – these are rhodium and palladium. The recovery and refining of platinum is similar to gold however the metal is more expensive. There are important physical properties:
- It reflects light well but not as silver or gold
- It has a naturally bright white colour which does not tarnish so is ideal for the setting of diamonds
- It is a noble metal which is only attacked by boiling Aqua Regia
- It is both malleable and ductile to almost the same degree as gold
- It takes a very high temperature to melt it. This sometimes presents a problem working with it
- It is a very heavy metal with a specific gravity of 21.43 therefore it is not suitable for large pieces of jewellery which might be uncomfortable to wear.
Platinum is not a hard metal in its pure state – it becomes much harder when it is mixed with copper, palladium or iridium. It is always a platinum alloy that is used in making jewellery. There is only one legal standard of 950 parts platinum in 1,000 parts of metal. This standard became law on 1st January 1975 and only since then has the metal been hallmarked. Before then items were marked with “PLAT” or “PT”.
This is harder and whiter than platinum. It is also more reflective. Its only use in jewellery is as a thin surface plating designed to give a hard, bright, untarnishable white surface to articles made of white gold or silver.