Gold karats describe the gold purity, or fineness, of any given item of gold, usually in reference to jewellery.
Because pure gold is inherently soft and highly malleable (an ounce of gold can be pulled into a wire 80km long!), it is usually alloyed with other metals such as copper, zinc, silver, nickel or palladium to give it greater durability and strength and make a more usable product. The higher the karat number, the greater the proportion of gold in that alloy.
1 gold karat means 1/24, or 4.166%, of the total alloy is gold. By extension, 10 karat gold consists of 10 parts gold (41.66%) to 14 parts alloy, while a 24 gold carat item is considered pure gold, as the following gold carat scale illustrates:
Besides its malleability making it unsuitable for most applications, gold is alloyed for a number of other reasons.
Combining gold with other, less expensive metals also reduces the overall costs of the item, while still retaining the general characteristics of the yellow metal.
Specific metals can also be added to gold in order to develop particular, unique golden hues, including ‘white’, ‘rose’ and ‘green’ gold. To produce white gold, metals like silver and palladium are used, while rose gold is achieved through copper additives.
Is mined gold 24K?
Gold-bearing ore doesn’t always contain pure gold as it is associated with other minerals such as sulphur, copper, lead and zinc within the veins where it is formed. It is generally found in its natural state to be approximately 75-85% pure, meaning naturally occurring gold is generally 18 karats to 20 karats.
It must be refined, purified and separated, using a range of beneficiation processes such as flotation, chemical precipitation and smelting, to reach higher purities, with 24 karat gold referring to a 99.999% gold purity.
Gold carat & gold karat: what’s the difference?
Confusingly, ‘carat’ and ‘karat’ are 2 different metrics that can both be used to describe gold quantity. However, whereas karat is a measurement of quality, carat refers to weight. Carat has a broader application to also describe gemstones; the term derives from the seed of a carob tree, which has a weight roughly equivalent to the smallest gemstones. In the early 20th Century, the weight of the carat was defined as 200 mg, or 0.2 g.
Karat, on the other hand, refers exclusively to gold purity.
Karats vs. millesimal fineness
Karats aren’t the only way to represent gold fineness. In Europe and elsewhere, gold fineness is described in terms of parts per 1 000, where 18 karat gold is described as “750”. This measurement of gold purity is known as millesimal fineness. Millesimal fineness is often preferred to karat analysis in gold-based application outside of jewellery, because it represents and differentiates fineness more accurately.
What is the purest gold ever produced?
The purest gold ever refined was a gold plate produced by the Perth Mint in Australia in 1957, with a millesimal fineness of 999.999 (equivalent to 99.999%). This is also called six nines fine. Such purity isn’t commercially available today.
The highest available purity is 999.99 (five nines fine), which the Royal Canadian Mint regularly produces in the form of commemorative coins. The karat rating is not used when describing gold of such purity, as it does not express fineness to the same accuracy as millesimal fineness.
How is gold refined?
The typical gold beneficiation process includes comminution, concentration, leaching, electrowinning, smelting and refining.
The comminution phase includes breaking down large chunks of ore into fine slurry or powder, typically through a crusher and ball mill. The material can further be sized through trommel screens and classified through cyclones or gravity concentration.
The slurry is then thickened with water and transported to leaching tanks, where a solvent (most commonly cyanide) is combined with oxygen to chemically dissolve the gold from the ore in a carbon-in-pulp plant. When carbon is added to the pulp, it adheres to the gold.
Following loaded carbon screening, the slurry is ready for elution, where caustic soda is applied to separate the gold from the carbon grains. The solution is then ready for electrowinning, which recovers gold from the leaching chemicals by applying an electric current through the solution that causes gold to collect on the negative terminals.
The gold is then ready for smelting. A flux is added to the gold and melted in a furnace heated to approximately 1 150° C. The flux separates most of the metal carried over from the electrowinning process. The molten gold is then poured into moulds to create dor bars. Still of relatively low purity at this point, the bars are then transported to gold refineries.
During gold refining, the dor bars are re-liquefied, and borax and soda ash are added to the gold, providing additional separation of metals to achieve purity of up to 99.9%.
The gold is then ready to be alloyed, as required by the final application.
How is gold karat price calculated?
To calculate gold karat price, you will need to know the current gold spot price as well the weight and fineness of the item. Using a 22-gram, 14-karat piece with a gold price of $1,600/o.z. as an example, here is how to calculate the gold karat price:
Item weight: 22 g
Purity: 14 karats (58.33%)
Gram price: $51,447 ($1,600/31.1)
Calculation: 22 x 51.447 = 659.859
This mean, the gold karat price of a 22-gram, 14-karat gold item is $659.86.
Having an understanding of what gold karats mean is essential in knowing the purity of gold, and will help you understand both the value as well as the durability of your gold