VIVIANITE is a mineral, exactly an iron phosphate, which is in nature in a crystalline form or in a earthy form. In this latter form it is also called "blue ochre" and is located near iron deposits, but curiously, it can also be formed in the presence of organic discharges (sewage), by reaction between phosphoric acid compounds present in excreta and the iron of the ducts or in waters. Use as pigment dates to centuries back in the areas where it could be found: for example in Roman paintings in Germany.
The watercolor thus prepared with this pure pigment presents important granulation.
Coloring agent: Hydrated iron phosphate