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What Does Carat Mean? Origin & Use in Jewellery

9ct , 9 carat , 18 carat or 24 carat (other carats are available…). But what exactly is a carat?

Origin of Carat

It may come as a surprise to know that the origin of Carat comes from the humble carob. A bean from the carob tree that is used as an alternative to chocolate. The carob tree is Mediterranean in origin and can be dated back to antiquity. But why do these small edible seed pods make such comparison units? This comes from them being incredibly reliable in weight and size. So one carob bean weighs virtually the same as another. This led to them being extremely useful as a unit of weight in ancient times.

There is documented evidence for this use of measurement from the ancient Greeks, following through to the 1500s when Latin alchemists were using the weight measurement, calling it carrutus. From here we get the modern derivative ‘carat’.

How much does a Carat weigh?

Pre-1913, the weight of 1 carat in the US was 205.3 milligrams. After this date, the weight was rounded to 200 milligrams as a standard ‘carat’, or ‘metric carat’ of weight. Several countries including Japan and parts of Europe were already using this standard of 200mg by then. 

142ct’s = 1oz (1 ounce ).

Carat can be used for either gold or gemstones. The importance is the weight of the actual amount of material. The base of this is full 24ct gold (solid pure gold is 24/24th’s). So the higher the carat, the more gold in a piece, with only 24ct gold being 100% gold.

Due to gold being a soft metal, other metals are added to it to increase its durability. Pure gold would be too soft and wear down too fast to make it suitable for most types of jewellery. In this sense, all gold is ‘gold alloy’ (a mix of metals) except 24ct gold. Most commonly, copper, zinc, and nickel are added. Though nickel less so these days and many gold alloys don’t contain it at all.