Colour

Throughout history, gold has been treasured for its natural beauty and radiance. For this reason, many cultures have imagined gold as a representation of the sun.

Yellow gold is still the most popular colour, but today gold is available in a diverse array of hues. The process of alloying—mixing other metals with pure 24 carat gold—gives malleable gold more durability, but can also be used to change its colour.

White gold is created through mixing pure gold with white metals such as palladium or silver. In addition it is usually plated with rhodium to create a harder surface with a brighter shine. White gold has become the overwhelming choice for wedding bands in the US.

The inclusion of copper results in the soft pink complexion of rose gold while the more unusual colours such as blue and purple can be obtained from the addition of patinas or oxides on the alloy surface. Black gold for example derives its colour from cobalt oxide.

Caratage

The weight of gold is measured in troy ounces (1 troy ounce = 31.1034768 grams), however its purity is measured in ‘carats’.

‘Caratage’ is the measurement of purity of gold alloyed with other metals. 24 carat is pure gold with no other metals. Lower caratages contain less gold; 18 carat gold contains 75 per cent gold and 25 per cent other metals, often copper or silver.

The minimum caratage for an item to be called gold varies by country. In the US, 10 carats is the legal minimum accepted standard of gold caratage, 14 carats being the most popular. In France, the UK, Austria, Portugal and Ireland, 9 carats is the lowest caratage permitted for an item to be called gold. In Denmark and Greece, 8 carats is the legal minimum standard.

Fineness

Fineness is another way of expressing the precious metal content of jewellery, and represents the purity in parts per thousand. When stamped on jewellery this is usually stated without the decimal point.

This chart shows some examples of the composition of various caratages of gold.

Notes:

The alloying metal compositions shown above are typical of those used by the jewellery industry in order to arrive to the colour / caratage combinations shown, but are not the only ways of achieving these combinations.

White gold compositions listed here are nickel free. Nickel-containing white gold alloys form a small/very small percentage of white gold alloys and generally contain other base metals such as copper and zinc.

The following are the common standards of fineness that are used:

.375 = 9 carat (England and Canada)

.417 = 10 carat

.583 (.585) = 14 carat

.750 = 18 carat

.833 = 20 carat (Asia)

.999 (1000) = 24 carat pure gold

Strictly speaking, 14 carat gold should be 583 (14/24 = .583333), but most manufacturers have adopted the European practice of making 14 carat gold, slightly over 14 carats. Thus, the fineness mark is 585 in most 14 carat jewellery.

Similarly, 24 carats should be 1.0 (24/24 = 1.00). However, in practice, there is likely to be a very slight impurity in any gold, and it can only be refined to a fineness level of 999.9 parts per thousand. This is stated as 999.9.

Accepted variations in purity vary from market to market. In China, Chuk Kam (which is Cantonese for ‘pure gold’ or literally ‘full gold’) still comprises the majority of sales and is defined as 99.0 per cent minimum gold, with a 1.0 per cent negative variations allowed.

(Source: World Gold Council http://www.gold.org)