Throughout history, gold has been treasured for its natural beauty and radiance. For this reason, many cultures have imagined gold to represent the sun.
Different Gold Colours
Yellow gold jewellery is still the most popular colour, but today gold is available in a diverse palette. 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 alloying 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.
Gold Carat
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 carat is the legal minimum accepted standard of gold caratage, 14 carat being the most popular. In France, the UK, Austria, Portugal and Ireland, 9 carat is the lowest caratage permitted to be called gold. In Denmark and Greece, 8 carat is the legal minimum standard.
Gold Purity
Fineness is another way of expressing the precious metal content of gold jewellery, and represents the purity in parts per thousand. When stamped on jewellery, usually this is stated without the decimal point.
This chart shows some examples of the composition of various caratages of gold.
| Caratage | Gold(Au) | Silver (Ag) | Copper (Cu) | Zinc (Zn) | Palladium (Pd) | |
|---|---|---|---|---|---|---|
| Yellow Gold | 9k | 37.5% | 42.50% | 20% | ||
| Yellow Gold | 10k | 41.70% | 52% | 6.30% | ||
| Yellow Gold | 14k | 58.30% | 30% | 11.70% | ||
| Yellow Gold | 18k | 75% | 15% | 10% | ||
| Yellow Gold | 22k | 91.70% | 5% | 2% | 1.30% | |
| White Gold | 9k | 37.5% | 62.5% | |||
| White Gold | 10k | 41.7% | 47.4% | 0.9% | 10% | |
| White Gold | 14k | 58.30% | 32.20% | 9.50% | ||
| White Gold | 18k | 75% | 25% (or Pt) | |||
| White Gold | 22k | N/A | N/A | N/A | N/A | N/A |
| Rose Gold | 9k | 37.5% | 20% | 42.5% | ||
| Rose Gold | 10k | 41.70% | 20% | 38.3% | ||
| Rose Gold | 14k | 58.30% | 9.2% | 32.5% | ||
| Rose Gold | 18k | 75% | 9.2% | 22.2% | ||
| Rose Gold | 22k | 91.7% | 8.40% |
Notes:
The alloying metal compositions above are typical of those used by the jewellery industry to arrive at the colour/caratage combinations shown, but these are not the only ways to arrive at 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 should be 583 (14/24 = .583333), but most manufacturers have adopted the European practice of making 14 carat gold slightly over 14 carat. Thus, the fineness mark is 585 in most 14 carat gold jewellery.
Similarly, 24 carat 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 tolerances on 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 tolerance allowed.
Gold Hallmarks
Gold hallmarks originated to show the purity of gold in a piece of gold jewellery and included the mark of the assaying office that certified the purity as well as the fineness or caratage of the gold. Later, trademarks that showed which goldsmith had manufactured the product were added.
Hallmarking gold jewellery was Europe’s earliest form of consumer protection, dating back to King Louis IX of France and Edward I of England in the 1200s. As craft guilds arose in these two dominant markets of Middle Ages Europe, state-appointed assayers examined precious metal goods. Their prescribed mark, and subsequently marks for individual goldsmiths and production dates, became a pre-requisite for gold items offered for public sale.
In 1327, King Edward III of England granted a charter to the ‘Worshipful Company of Goldsmiths,’ headquartered in London at Goldsmiths’ Hall. The English term ‘hallmark’ originates with this hall and its official marks.
In the UK, all gold products sold on the home market must now be hallmarked at one of the four assay offices in London, Birmingham, Sheffield and Edinburgh each of which has a distinctive mark. Articles weighing less than 1 gram are exempt.
Similar systems to clearly identify the caratage and origin of gold items have been introduced over time and around the world. But each nation has created its own requirements and distinctive gold hallmarks and markings.
In the US, an item’s caratage(/karatage) may be identified by independent signage close to the piece of jewellery or verbal information. It does not have to be marked on the piece itself. If an item is marked, it must also have a trademark stamp in close proximity to identify its origin. In the US, the fineness in parts per thousand is often used to indicate purity instead of caratage.
In many other countries, including in Italy, India and China, jewellery hallmarking is voluntary. Gold manufacturers apply their own marks to their creations, to attest to their origin and caratage. This practice pre-dates the modern Italian state in the traditional centres of gold craftsmanship of Italy, such as Arezzo, Vicenza, Valenza or Bassano del Grappa. Here, the manufacturer’s identification mark is composed of a number and the first two letters of his region, as for example, 1 AR for Arezzo. In Switzerland, hallmarking on jewellery is optional except for metal watch cases.
In an attempt at standardising the inspection of precious metals, in 1972, a group of European nations signed the Vienna Convention on the Control of the Fineness and the Hallmarking of Precious Metal Objects. Most European nations are party to the Vienna system and a number of other nations monitor it. It introduced a Common Control Mark (CCM).
Each member country agrees to allow goods marked with the CCM mark to be imported without further testing or marking if such articles would normally qualify for a domestic mark. To be marked with the CCM a precious metal must bear a fineness mark, a responsibility mark and an Assay office mark. The CCM thus represents an additional protection and quality mark.
