The 18 carat specification for gold is a unit of measurement for the proportion by weight that gold occupies in the overall mixture of an alloy. The percentage by weight (also fineness) of gold is given in 1/24 parts. The highest purity of gold, i.e. the highest proportion of pure gold by weight within a gold alloy, is achieved at 24/24 parts by weight, i.e. 24 carats. However, since possible impurities can never be completely eliminated, even 24-carat gold only achieves a purity of 99.99%. However, 24 carat gold is not suitable for processing jewellery, as it is much too soft and bends easily. Therefore, 18 carat or also called 750 gold with 75% gold content is the highest quality gold alloy that is suitable for processing jewelry.