Understanding Carats: The Seed of Value in Jewellery

This spring time many of us are struggling to get seeds into the sodden ground. Our connection with seeds is deeply ingrained (sorry!). These familiar things have been used by us humans for more than growing food and useful building materials – they have underpinned our assessment of the things around us and been the basis of our trading measurements and processes.

The Ambiguity of ‘Carat’

I was recently asked what the term ‘carat’ means when used in the jewellery world. Like many things in this trade – it’s strangely ambiguous, plant based and can refer to two different things. A carat can be a unit of mass (weight) or a unit purity.  However you’re using it, the word derives from the Greek word for the seeds of a carob tree.  In ancient times, carob seeds were used as counterweights when weighing gems and jewellery because they were plentiful and have a uniform weight.

In some countries the spelling is “karat” is applied to the purity measurement for gold to distinguish from “carat” the unit of mass for gemstones. This sensible move does make things clearer – thank you America – but here in Blighty, we sling the terms together and rely on the context to give away the meaning of the word.

Measuring Gemstones and Gold Purity

When describing a unit of mass in gemstones, a carat equals 0.2 grams.  The carat is  abbreviated as “ct”. Certain gems such as diamonds, have a premium price if they weigh one  or multiples of a carat (or neat fractions of a carat such as a quarter or half).This is handy knowledge when it comes to buying as you will pay markedly less for a 0.99 ct compared to a 1ct diamond. 

We all know that size isn’t everything, but if the occasion calls for a show-stopping gemstone on a tight budget, it is handy to be armed with some knowledge of gemstone mass. Different gems are priced according to their rarity and quality, but they are all sold by their weight. Two different types of gems of the same physical size can have very different weights to each other. Sapphires for example are dense heavy stones when compared to quartz or tourmaline.

Interestingly, pearls are traditionally weighed in units of ‘grains’. This was originally the equivalent weight of a grain of wheat. 24 grains made a pennyweight and 20 pennyweights made a troy ounce. Troy ounces are the traditional unit for gold and other precious metals, Investment coins and bullion are traded using this weight which is the equivalent of 31.1 grams. 

Confusingly, ‘Carat’ is also used to describe the purity of gold alloys. In the jewellery trade, gold is used in different qualities. These qualities are described with a measurement of purity, with 24 carat being pure gold (24 parts gold in a total of 24). The different qualities have different working properties and appearances, giving a range of varying uses.

Certain carats of gold (22, 18, 14 and 9 carat) are recognised qualities for the U.K. hallmarking process. 9ct gold, for example,  is 9 parts gold in 24. The remaining metals in the mix or alloy are usually silver and copper. 9ct  is a hard-wearing gold quality, and less expensive than the higher qualities because it contains less gold. Generally speaking, the more silver added to the alloy, the whiter the colour. With 18ct gold, ‘white’ gold is created using other white precious metals such as palladium. Rose golds are made by adding more copper in the alloy. 

Advantages in Jewellery Making

Different carats and alloys of gold also have different melting points, which is a huge advantage in the making process. When joining two pieces together, I use a process called soldering, which requires heating the metal to a high temperature and introducing a small piece of solder (gold of a slightly different alloy with a lower melting point). This solder melts and bonds the two pieces together. The subtleties between melting points can be used to advantage when creating jewellery, new pieces are added without re-melting existing joins etc. This enables me to create complicated structures piece-by-piece and repair old items seamlessly. 

Pure (24 carat) gold is not usually used in mainstream jewellery making as it is very soft, very valuable, not as resilient to hold stones and take daily wear and tear. There are exceptions to this however; traditional crafting techniques for Indian jewellery for example, can transform the qualities of pure gold, into pieces that withstand generations of wear. The trade-in value of this jewellery  remains high too, because the gold is not alloyed or ‘diluted’. 




This was written and published as part of the ‘Hidden Gems’ series of articles by Erica Sharpe for the Western Daily Press.