Sodium sulphate and potassium hexacyanoferrate, polarised light micrograph. Sodium sulphate is an inorganic neutral salt that is used as a bulk filler in home cleaning products and as a fining agent for removing small air bubbles in molten glass. Potassium hexacyanoferrate is a bright red-orange soluble salt. It is used in histology where it transformed into the blue pigment Prussian blue in the presence of iron. This image is a crystalline film made from a mixture of sodium sulphate and potassium hexacyanoferrate. Magnification: x70 when printed 10 centimetres wide.