Gold Technical Information
Common Name: Gold
Latin Name: Aurum
Chemical Symbol: Au
Gold is non-reactive to water or oxygen.
Gold is extremely ductile. A single gram can be drawn into a thread 3500mtrs long!
Gold is one of only 2 coloured pure metals in existence – the other is copper. All other pure metals are grey or white in colour.
The term Carat (ct) (which is called Karat (k) in Germany and the US) is a unit of weight measure equivalent to 200mg ie 0.2 or 1/5th of one gram. It is used to measure the weight of gemstones and diamonds. It has also come to be used as a measure of the Purity of gold alloys with 24ct being defined as pure gold. In Australia it is common to use the terms 18ct, 9ct etc rather than 18k, 9k, when describing the purity of Gold.
Gold Purity
The Purity of gold alloys can be measured in carats/karats which indicates how many parts out of 24 is gold. Pure gold ie 24ct gold is 24 parts out of 24 gold. 18ct gold is 18 parts out of 24 gold. 14ct gold is 14 parts out of 24 gold etc. The rest of the alloy is made up of other metals.
Gold purity can also be expressed in terms of fineness which is simply parts per thousand of pure gold.
Some examples of Gold Purity
18ct is 18/24 which is equivalent to 750 parts per thousand pure gold called 750 fineness. Hence you will see 18ct gold often stamped with the number 750.
Similarly, 14ct gold is 583.3 parts per thousand pure gold
and 9ct gold is 375 parts per thousand pure gold.
In Europe the most popular alloys are 18ct and 14ct
In USA 14ct and 10ct
In Australia 18ct and 9ct
India, Middle East, South East Asia 22ct
In China and Hong Kong 23.76ct is popular (almost pure gold)
At eJeweller.com.au we supply jewellery in 9c, 14ct and 18ct gold and also silver and platinum.
Specific Gravity of Gold
Specific gravity (SG) is used to compare the density of different materials in relation to water. If a given volume of a substance has a specific gravity of 2 it means that it is twice as heavy as the same volume of pure water. You can see in the following table some SGs of various common alloys of gold. Note that these are estimates given that there is more than one ‘recipe’ for each gold karatage.
24ct Pure Gold – SG = 19.32 (ie 19.32 grams per cubic centimetre)
18ct Gold Alloy- SG = ~15 to ~17 (red golds near the lower end, white golds near the upper)
14ct Gold Alloy- SG = ~12.9 to ~14.
9ct Gold Alloy- SG = ~10.9 – 12.7
Some Other Metal Specific Gravities:
Silver – SG = 10.5
Sterling Silver Alloy- SG = ~10.3
Copper – SG = 8.9
Platinum – SG = 21.4
Palladium – SG = 12
950 Platinum Alloy- SG = 20.1
Why alloy gold with other metals?
Pure Gold is always yellow but Gold is rarely used in its pure form (24ct) for jewellery because it is just too soft. Pure gold is not very durable and scratches and dents easily. It is the addition of other metals that gives us the different caratages, colours and changes in hardness strength and malleability.
White gold is created by alloying yellow gold with with silver, nickel or palladium. Rose or red gold is achieved by alloying with copper. To increase the hardness of Gold, nickel or titanium is added.
Adding copper to gold makes the alloy redder. Any other metal, when added to gold, will have a whitening (or bleaching) effect. The strongest effect comes from Nickel, Palladium and Platinum, a weaker effect is seen from Silver & Zinc. The other metals have a minimal effect.
So for any particular caratage we can vary the colour by varying the amounts of copper, silver, nickel, zinc etc. whilst maintaining the required amount of pure gold for that particular caratage.
Colour is not the only property affected by adding these other metals.
Generally speaking, as the caratage decreases so does the density of the alloy and also the melting point. Conversely, as the caratage decreases the hardness & strength increase especially down to 18ct. Further reduction from 18ct to 9ct only has a small further effect.
White Golds for jewellery were developed around 1920 and were intended to be used a s substitute for Platinum.
Most commercial white gold alloys are a mixture of gold, nickel, silver zinc with copper sometimes added to improve malleability. This additional copper takes the alloy colour to a slightly yellow/brown tint. To overcome this, white gold jewellery is usually rhodium plated. Rhodium is tarnish resistant and gives a good white colour.
Some reasons for adding other metals to Gold
Nickel – increases hardness & whiteness
Silver – increases whiteness
Zinc – increases melt fluidity for casting detail, improves malleability
Copper – increases redness
Gold Caratage and its Effect on Price
Jewellery is commonly made using 9ct, 10ct, 14ct and 18ct gold.
When buying an expensive diamond ring we recommend using 18ct gold given that the saving you will make on the overall cost of the diamond ring by choosing 9ct gold is not significant.
Conversely, when buying a small diamond or gemstone ring then the type of gold is important as its cost may be a significant proportion of the overall cost of the diamond or gemstone ring.
The other consideration is one of appearance. Generally speaking 18ct yellow gold is more yellow than 9ct yellow gold.
Common types of gold alloy in increasing price order
9ct Yellow Gold
9ct White Gold
14ct Yellow Gold
14ct White Gold
18ct Yellow Gold
18ct White Gold
Rose or Red Gold is usually a bit more expenseive than Yellow Gold.
History of Goldsmithing
In what is today known as Bulgaria in southeastern Europe, and in what is today known as southern Iraq (the Sumer civilisation) it is believed jewellery production began over 5,000 years ago.
The Minoan Civilisation of Crete (3000BC – 1000BC) produced the first known cable chain.
We hope the above information has given you an insight into the various types of Gold Alloys. Please follow the links for more information on particular topics, or click here to browse our beautiful Gold Wedding Rings.
If you require clarification, feel free to contact us with your question. At eJeweller.com.au we have jewellery & gemstone experts on hand happy to help with your enquiry.