The main reaction in colour pigment production takes place in the ‘coupling’ vessel. So named as a type of coupling reaction occurs here to form a synthetic ‘azo dye’, which is then converted into different colour pigments in subsequent process steps. An agitator in the tank ensures constant mixing of the azo dye. Additionally, ice is added for cooling, as otherwise the individual components of the reaction would decompose. Level measurement is required to ensure a smooth process flow.