Precious metals just as with most precious stones occur as mineral deposits in the ground and require extensive mining and refining techniques to obtain a 'fine' finished product. Very often though precious metals are found in small pebble or grain deposits, popularised by gold panning in rivers.
A fine finished product would be a precious metal that has had all other materials / ores / impurities removed and is in a highest possible Carat and is in it's most pure form. Although it is almost certainly impossible to remove every single impurity, fine metal is 99.99% pure.
Carat is the unit of measuring a precious metals compound mixture. ( not to be confused with carat weight of precious stones). Caratage of a metal is calculated in percentage. Although it is displayed and referred to in it's decimal value and / or out of a thousand parts. An example in silver most commonly used is known as 925 and is actually 92.5% fine silver and 7.5% alloy metals Copper and Silver are naturally found with gold in various amounts. If there is moer than 20 % content of silver in native gold then it is referred to as Electrum. Copper and Silver are thus the primary inclusions to fine gold to alloy it down.
There have been several other alloys added into the mixes throughout history and still today the modern alloys are mixtures of several metals along with the primary alloys. Nickel, Tin and Zinc have been used in the past, but due to the poisonous nature of Nickel it has almost been abolished as an alloy for jewellery and it is now illegal to have more than a few micrograms present in jewellery like ear-rings under guidance of the Nickel Directive. Modern casters use Silicon as an alloy for casting low carat gold, and some white gold can still be found with a trace of nickel as an alloy.
** the lower the carat the harder it is..... this statement is only true based on specific alloy content and percentage, some alloy mixtures can easily make even a higher carat gold (18ct) harder and more durable than the lower carat (9ct). True properties of each gold mixture can vary from supplier to supplier and country to country, thus making this an interesting and important point to consider when purchasing international metal products.
Gold quality is measured by percentage of gold content. Another system is by calculating it out of 24 parts.
fine gold is considered pure and is 99.99% native gold and written or marked as 999 or 24 carat
22 carat could be marked 916 and be 91.60 % pure gold
18 carat could be marked 750 and be 75% pure gold
14 carat could be marked 585 and be 58.50% pure gold
9 carat could be marked 375 and be 37.5% pure gold
Platinum hallmarks are either:
850 (85% pure) and could be marked PLAT
900 (90% pure) and could be marked PLAT
950 (95% pure) and could be marked PLAT
999 (99.9% pure) and could be marked PLAT
The Family Group of Metals classed as Platinum include Rhodium, Iridium, Platinum, Osmium, Palladium and Ruthenium.
Silver caratages are:
800 is 80% native silver
925 is 92.5% native silver and is known as sterling silver
935 is 93.5% native silver and is known as britannia silver
fine silver is 99.99% pure and known as fine silver
all the above carats can be stamped SIL or SILVER