Rhodium is a chemical element that belongs to the series of transition metals and has a silvery-white, metallic colour. The precious metal is listed under the symbol Rh and the atomic number 45 in the periodic table of the elements. Rhodium is very hard and since it is a very inert substance, it is difficult to extract and accordingly expensive. The degree of hardness of rhodium exceeds that of gold and platinum, but it is also tough, so that it can be worked by mechanical means. Basically, rhodium is comparable to other platinum metals in terms of appearance and properties. The precious metal is also popular in many areas of application due to its good catalytic properties. Rhodium alloys are used, for example, in vehicle catalytic converters for the reduction of nitrogen monoxide. Rhodium is interesting for the jewellery industry because it can be used as a coating for high-quality jewellery, in spectacle frames and also for watches. This coating prevents the metal from tarnishing, which can happen especially with silver jewellery. If the element is used to coat jewellery, it is called rhodium plating.