In the diazotization process, the individual raw materials for colour pigment production are prepared so that they will react to become diazonium compounds ready for the subsequent ‘coupling’ vessel where they form the final crude pigment or ‘azo dye’. The basic starting materials for these compounds are hydrochloric acid, water, sodium nitrite and the diazo component (usually aniline). To preserve the material quality during formulation, the mixture is kept cool by adding ice or via a cooling jacket. During this process, the level must be carefully monitored and kept constant.