Karats and Carats

The words ‘Karat’ and ‘Carat’ used in jewellery have both developed from the same root which is a historic use of the carob bean as a base unit of weight. Carob (which you might have heard of as a substitute for chocolate) is a seed pod vaguely like a cocoa pod and within it are beans which are edible. They are quite consistent with respect to their size even when grown in different countries and climates and so they came to be used as a base weight unit by the Greeks many years ago and this practice was common in lots of other countries too. So they would put these beans in one side of the scales and the thing they wanted to weigh in the other side and declare that the item weighted ‘2 carobs’ for example.

Over the years, the word ‘carob’ became corrupted to be spelled ‘carat’ or ‘karat’. ‘carat’ and ‘karat’ came to mean different things although ‘karat’ is not really used much here in the UK.

The unit of weight known in both the UK and the USA as a ‘carat’ is now defined as being equivalent to 200mg. So when say, a diamond is weighed this weight in carats can simply be converted into grammes – so this unit it is simply about weight. So what that means is that if a diamond is a particular weight – say 0.25cts, then this does not necessarily mean that it will be of a specific mm size. The mm size will depend on the shape and cut of the stone. And if the stone is cut into a round brilliant cut ‘classic’ diamond, it can still be proportioned differently. For example, a very deep stone from the top of the table to the bottom of the tip or culet will be heavier for its mm size than a very shallow one.

So what about the carat of gold? These days, this kind of carat/karat has nothing to do with weight at all and refers to the purity of gold. If gold is completely pure, it would be 24 carat/karat gold which would mean that it is 24 parts in 24 parts gold. Gold is a very soft and malleable metal which is one of the reasons that it is so popular for jewellery – we can form it using the right tools and skill into all sorts of lovely jewellery shapes. However, 24ct gold is so soft that a gold bangle made from 24ct gold could easily be reshaped by hand which is not ideal for every day wear. So we alloy this with other metals to make the metal harder and more durable and resistant to scratching and reshaping. In the UK we use 18ct and 9ct gold (which are 18/24 parts or 75 percent gold and 9/24 or 37.5 percent gold). In the USA the more common alloys are 14ct and 10ct.

When gold is alloyed with other metals, the other metals in the alloy not only improve its performance for durability, but also alter the exact ‘colour’ of the metal. Pure gold is a rich yellow colour and it is not possible to get white 24ct gold for example because pure gold actually is this rich yellow colour. But with, say 18ct gold, this is alloyed with other metals like silver, copper and zinc for example (there is a long list of metals used in these alloys actually!) and these other metals give the alloyed gold different properties. with a high proportion of copper and silver, rose gold is made. With a high proportion of silver and often platinum and palladium, white gold is made. Depending on how this alloy is made, there can therefore be different alloys which can all call themselves ’18ct white gold’ and the exact colour will be effected by the make-up of the alloy. Here, for example, we use an 18ct white gold alloy which is naturally very white – a light gun-metal white whilst some white 18ct gold that I have seen seems much more yellow than our alloy. In addition to the colour of the alloy itself, rhodium plating is also another factor in the colour of white gold if it is used to coat the finished white gold piece of jewellery – but that is something that I will write a separate article about or you can see some information via the link in the next paragraph.

There are some pictures showing the different colours and carats of gold that we normally use here (although we can make jewellery in other carats too).

I hope that has helped clear up some understandable confusion!