Precious Metals
Introduction
Gold, Silver and Platinum are all considered to be precious metals. Gold & Silver have been highly prized for thousands of years. In the Egyptian culture Gold represented the sun god Ra.
In early times the yellow of Gold was associated with the fire of the sun and the white of silver was related to the moon. The original Latin name for Silver was luna, meaning moon. This was later changed to ARGENTIUM, which means white & shining. Although used by pre-Columbian Indians in South America to make small ornaments it wasn’t until the 18th Century that the true worth of Platinum was recognised.
Gold and Silver deposits were widely distributed throughout the world which explains why so many different civilisations discovered and used these metals to produce jewellery and decorative objects. The Ardagh Chalice, Tara Brooch and the Cross of Cong are beautiful examples of early metal work in Ireland.
Gold & Silver also assumed a monetary role, lasting for over 2000 years, and were widely used in trade to accumulate wealth.
Precious metals used by today’s Goldsmiths and Silversmiths are supplied by bullion dealers in the form of sheets of various thicknesses, grain for casting, and wire of many shapes and lengths.
Silver
- Silver: Ag
- Copper: Cu
Silver in its commercially pure form is referred to as Fine Silver and contains at least 99.9% Silver Ag.
Fineness is used to describe how much precious metal is present in the metal or alloy in terms of parts per 1000.
- Commercially fine silver is of a fineness not below .999
- Sterling Silver is of a fineness not below .925
Therefore Sterling Silver is an alloy containing 925 points per 1000. The remaining 75 points is usually, but not always, copper.
Tarnishing of Silver
When Silver is exposed to the atmosphere it tarnishes. Initially the surface becomes covered with yellowish-brown flecking which gradually becomes a continuous film and darkens until it becomes black. At this stage the tarnish film is quite thick and requires considerable effort to remove and to restore the surface to its original lustre. The film is Silver sulphide and is formed principally by the reaction between hydrogen sulphide gas (H2S) and Silver in the presence of oxygen or moisture. Other common causes of deterioration are human perspiration, which is high in sodium chloride (common salt), perfume, shampoo and deodorant sprays. There are also some foodstuffs such as pickles, onions, garlic and fruit juices, which release high levels of acid and/or sulphur compounds.
Most wrapping papers contain chlorides from the bleaching process used in paper making and will react with moisture/dampness to form hydrogen sulphide causing the finish of Silver wrapped in such papers to deteriorate.
Glue used in storage boxes and cellophane bags is another cause of tarnishing.
Removal of Tarnishing
Tarnish removal can be carried out either mechanically or chemically. Mechanical removal consists of abrasion with jewellers rouge made up as a paste and spread on with a suitable polishing cloth. This not only removes the tarnish it also polishes the silver surface. A number of pastes or impregnated cloths are available for example the Goddards range of products could be considered.
Chemical cleaning involves immersion in a solution that dissolves the tarnish film. The Goddards range is also worth considering.
NB: Both of these methods will damage or remove any Gold Plating on the item.
Protecting Against Tarnishing in Your Store
Remember that Silver products that are exposed to the air will tarnish. This process cannot be prevented completely; elements such as sulphur, moisture, oxygen and chlorides, which accelerate the tarnishing process, are all around us.
Anti-tarnish square papers (little black square papers) help to inhibit tarnishing by absorbing hydrogen sulphide and preventing it from attacking Silver.
Sealed polythene bags provide protection against the atmosphere and its easy to see the item within.
Staff should carefully remove finger marks from silver items after handling during a sale (Remember to be gentle with Gold Plated areas)
Silver display items should be sold to customers and then replaced with the back-up item that has been closed while in stock.
Gold
-
Gold: Au
-
Copper: Cu
Gold in its natural form is yellow. The fineness is parts per 1000 as with silver.
Pure gold has a fineness of 1000. In the United States the minimum standard that can be represented as gold is 10 Karat Gold.
-
10 karat Gold = .417 parts Gold and the balance consists of alloys
-
14 karat Gold = .585 parts Gold and the balance consists of alloys
-
18 karat Gold = .750 parts Gold and the balance consists of alloys
The word karat evolves from the Arabic word “Kỉrật” which is the name of the seed of the locust bean tree. Because these seeds were similar in size and weight, they were used by African Traders for weighing purposes.
-
Pure Gold is known as 24 Karat.
-
10 Karat is 10 out of 24 parts or 41.7% Au
-
14 Karat is 14 out of 24 parts or 58.5% Au
Pure gold is too soft to be used in the manufacture of jewellery. Its main use has been for coinage and various industrial purposes.
The karat gold standards are based on the gold-silver-copper (Au-Ag-Cu) alloy system. Other additions, usually Zinc (Zn) may also be present in lower karatage alloys.
Variations in the proportions of Silver, Copper and Zinc (but not Gold) used, can give a variety of colours from green to yellow to red in the same Karatage.
White Gold
The commercial use of White Gold was developed in the early 20th century as a substitute for Platinum which is a considerably more expensive metal.
Only Palladium (Pa), Nickel, and to a lesser extent Manganese (Mn), give a significant whitening effect, good tarnish resistance, and allow good formability to work and for the setting of precious stones.
Small additions of Copper, Nickel, Zinc, Manganese, Platinum and Silver may be present in alloys from all Karatage.
Note
Most White Gold jewellery is rhodium plated. This protects the polished finish on the white gold and gives it a whiter sheen, (polished white gold has a greyish colour).
This applies to jewellery items produced in parts (ie; in diamond rings with a white gold head and a yellow band, the white gold head will be rhodium plated) and to items such as white gold wedding bands, white gold pendants etc.
With gold prices rising to a 20 year plus high some bullion suppliers are using less palladium and more copper/silver in their white gold alloys. Issues with your customers will arise when the rhodium plate finish wears off and the underlying gold has a yellowish hue. Be careful when purchasing white gold at apparently low prices.
Tarnishing
We have covered the causes of silver tarnishing. Lower karatage gold alloys also tarnish. Occasionally customers will complain that their gold jewellery has blackened their skin and clothing. This is due to a higher mix of silver and copper and other base metals in the alloy. As we know these base metals are affected by sulphur bearing gases, soaps, cosmetics and human perspiration (some people are more affected than others).
Platinum
Platinum group metals are mainly used for industrial purposes e.g. Platinum catalysts are found in automobile exhausts. Platinum jewellery represents only 7-10% of world Platinum production.
The karatage system does not apply to Platinum. It is known as:
-
Platinum 850
-
Platinum 900
-
Platinum 950
-
Platinum 999
The most common Platinum standard used in Ireland is Platinum 950. The primary alloy used is copper.
Useful Information
-
Gold, Silver & Platinum are known as precious metals. They are sometimes referred to as noble metals by craftspeople.
-
Copper, Zinc and Brass are known as base metals in the jewellery industry.
-
Karat is the measure of fineness in gold jewellery
-
Solid Gold or gold means fine gold. Items made from gold alloys should be referred to as such, for example 10kt Gold etc.
-
Gold filled or Rolled Gold Plate are the same type of product and are made by fusing a layer of a gold alloy to a base metal alloy by rolling as sheet or drawing as wire.
-
Gold Plated means that a layer of gold has been applied to part or all of the item by means of electroplating.
-
Sterling Silver is 925/1000 fine silver and 75/1000 base metal (usually copper)
-
Nickel Silver is a combination of nickel, copper and zinc, it contains no silver
