The manufacture of vermilion in the wet way is founded on the conversion of metallic mercury or its compounds into mercuric sulphide by heating with alkaline sulphides, such as ammonium sulphide and liver of sulphur. The product always contains uncombined sulphur, which is eliminated by treatment with alkalis. Apart from the danger to the health of the workmen caused by the poisonous mercury vapours, which are present in rooms where mercury or its compounds are heated in apparatus even of the best construction, and which is not to be feared in a wet process, the vermilion prepared in the latter manner has a finer and brighter shade than that prepared by a dry process. The greater cost of the wet process is covered by the higher value of the product. The starting point of the wet method may be either metallic mercury, black mercuric sulphide or another mercury salt. When metallic mercury is used, according to an old process, 100 parts are ground with 23 parts of flowers of sulphur and a little caustic potash solution to a homogeneous mass, which is then heated with a solution of 53 parts of caustic potash in an equal quantity of water, the evaporated water being continually replaced, until the colour changes from brownish-red to the fiery red of vermilion. When the colour approaches the desired shade a careful watch must be kept, and immediately the proper shade is obtained the heating must be stopped. If it is continued beyond this point for but a short time, the vermilion at once loses its fire and cannot be again brightened. An interruption in the heating is equally harmful, a dull shade being produced. When the proper shade has appeared, the contents of the vessel are poured into a large quantity of water. The vermilion is then washed with dilute caustic potash and afterwards with water until the alkaline reaction disappears. It is finally dried. The alkaline solutions obtained in this process contain considerable quantities of mercury in solution. They are collected, and when a sufficient quantity has accumulated the mercury is extracted. Barff recommends the following method: Mercury is rubbed with ⅙ to ⅕ of its weight of sulphur until a uniform grey powder results. This is heated in a porcelain dish with caustic potash solution (133 parts of potash in 150 parts of water) at 45° C. until the powder has become bright red. Heating above 45° C. is to be avoided; it would impart a brown tinge to the vermilion.