Any alloy is a mixture of two different metallic elements. Pure gold is usually mixed with silver, copper, and other admetals to produce the required working properties, such as durability.
Most gold used in jewellery is an alloy, and in most countries there are standard alloys which are legally recognised, and can be tested and stamped with an assay mark to guarantee its gold content. Even so-called pure gold is actually an alloy as it is almost impossible to eliminate all traces of impurity economically. Many people inaccurately describe 99.9 gold as pure. The Royal Canadian Mint proudly produce and market 99.99% fine gold coins and bars. Even these are not completely pure.
Gold Coinage Alloys
The very first gold coins, made over 2,500 years ago were sometimes made from gold which was as pure as ancient technology could manage. Others were made of electrum, a naturally occurring alloy of gold and silver, in which case the proportions of the alloy would be quite variable, as one would expect.
As metallurgy improved, most coins up to medieval times were made of relatively pure gold, typically 23 carats (95.83%) to 23.5 carats (97.92%). In those days, most gold coins did not circulate in daily transactions, but were more of a store of value, so the fact that "pure" gold is quite soft was of no practical important.
In modern times (approximately the last 200 years), most countries have standardised on either 90% (21.6 carats), or 91.66% (22 carats). When gold coins started to be used more frequently, as in circulation, it became more important that they should be durable, in which case they needed to be alloyed. The commonest admetals in gold alloys are silver and copper, although other metals can and are added for various reasons, some admetals occur as unrefined "contamination" in the original ores. In many cases,it was considered too expensive to fully refine, and many contaminants were tolerated and accepted providing they did not adversely affect important working or other practical properties.
Non Circulating Modern Gold Bullion Coins
The first modern bullion gold coin was the Krugerrand, which was, and still is, made of 22 carat gold.
The Royal Canadian Mint were the first to introduce "fine" gold coins, with their first gold maple leaf coin in 1979. These first issues were made of 99.9% pure gold, until 1983, when the R.C.M. started making its gold maples form 99.99% pure gold. Later, in 2007, a "five nines" version (99.999%) pure was also introduced.
A number of other countries and mints now make gold bullion coins, either in 22 carat or "fine" gold, some countries, such as the U.S.A. produce gold bullion coins in both alloys.
Red and Yellow Gold Alloys
Pure gold is very yellow. Ancient coins invariably contained some silver, so retained a yellow colour, Only in fairly recent times has gold been refined to near pure, so it is now quite common for some coins to contain only gold and copper, without any silver. This alloy is known as "red gold" for the obvious reason that it appears quite red compared with pure gold or gold alloys containing silver. There are of course many different compositions possible for "red gold", common one include 9 carat, 10 karat, 14 carat, 18 carat, and 22 carat.
Some people have a preference for one colour over the other. We actually prefer yellow gold alloys, as they look more natural, and more like "real gold". Red gold alloys can look very cheap and coppery, especially in lower carat alloys.
On numerous occasions since 2000, we have told the Royal Mint that it would be preferable from the viewpoint of most numismatists, and probably, most people, if they would resume the practice of including some silver in the gold sovereigns and other gold coins. The Royal Mint, being the Royal Mint, stubbornly refuse to accept any advice from mere coin dealers such as ourselves, they rather vainly think they are the experts, and therefore know best. Besides silver costs more than copper, so eliminating any silver content save a few pence per coin. We think this is a stupid and short-sighted policy.
Other Gold Resources
We have a number of other pages which may be of interest to you.
Modern Gold Sovereign Alloy Content (22 Carat Gold)
Bullion Coin Selector Page
18 Carat Gold Alloy Content
9 Carat Gold Alloy Content