The fineness is an important piece of information for jewellery, because it indicates to what extent the valuable basic element is contained in it. The fineness is therefore the standard value for how high the quality and also how expensive a certain product is. More precisely defined, the fineness determines the proportion by mass of the highest-grade precious metal contained in an alloy. The unit of measurement of the fineness is the per mil value, whereby the total mass is represented by 1000 parts. For the fineness, there are common content specifications, but no compulsory regulation. Thus, jewellery can be produced theoretically with very little precious metal or with a particularly high fineness. For gold, the usual purity grade is 995 per mille, which is used for the 12.44 kg bars for international trade. For the jewellery trade, gold alloys of 8 K, 14 K or 18 K are common. In these alloys, copper and silver are used in addition to the gold, which makes the gold stronger and gives it a different colour.