Gold Purity & Gold Density

Gold Density

With a density of 19.32 grams per cubic centimetre, gold is one of the densest metals on Earth. This is just one of the reasons gold is so desirable to humans is its high density.

Gold’s density is sensational. Anyone that has held physical gold in their hands understands the unique, and undeniably impressive, feeling of weight that it conveys. Even a small bar, not much bigger than a credit card, feels much heavier than one might expect.

Density can be defined as the ratio between an object’s mass and volume. Scientifically, this would be the ‘unit mass per unit volume’ and is usually quoted in grams per cubic centimetre.

To get technical, this is sometimes also known as ‘specific gravity’, which is a unified ratio of density with water. Gold’s specific gravity is 19.3; simply put, you would need more than 19 times the equivalent volume of water to have the same weight in gold.

Gold alloys, such as products of 9, 14, 18 and 22 carat purity, will have slightly lower densities than a pure (24 carat) gold coin or bar due to the other materials being mixed with gold. A one ounce, 24ct gold coin, will be smaller than a one ounce, 22ct coin for example, because it is denser. The density will then depend on the metal that has been used in the alloy.

Gold Purity

Pure gold is extremely soft and malleable. It is because of this that manufacturers, typically jewellers, often mix or alloy pure gold with other harder base metals. Without knowing a gold article’s precious metal content it is difficult to arrive at a true valuation.

To quantify this there are two major systems that measure purity. They are carat (karat in the US), and fineness. Both carat and fineness give figures that indicate the proportion of pure gold to other base metals in gold jewellery and products.

Gold carat

Carat expresses the proportion of gold to other metals in parts of 24. In this system, 24-carat is pure gold. 9-carat is nine-parts gold: the remaining fifteen parts of the 24 being composed of other metals.

Gold fineness

Fineness, in gold, silver and other precious metals, expresses the percentage of gold to other metals in parts per thousand. It is therefore a more precise scale than carat. In this system, 999.9 is pure gold. 9-carat gold, nine parts gold to fifteen parts other metals, is .375 fineness.

In the UK, with the exception of coins and pure gold bars, any manufactured gold products weighing over 1 gram or 0.0321507 troy ounce must be hallmarked with the item’s fineness.

How many carats is pure gold?

Both 24-carat and 999.9 fineness are generally accepted as 100% pure gold. Despite this, in truth it is impossible to produce 100% pure gold. This is why, in common terms, pure gold is 999 or 999.9 not 1,000 fineness.

The purest gold ever was made in 1957 by Australia’s Perth Mint. This was 999.999 fineness, known as ‘six nines fineness’. It has since been used by the Royal Mint as its benchmark for purity. 995 fineness is the minimum allowed purity for gold investment bars and is used as raw material for further gold alloying. The London Bullion Market Association undertakes gold testing and produces a ‘Good Delivery List’ that specifies standards for gold investment bars, which includes the required fineness.