Pozzolana is ground volcanic ash composed of siliceous and aluminous material from Pozzuoli, Italy.
Pozzolana (or pozzolan) is an Italian word, named from Pozzuoli, the place near Naples where pozzolan was first mined and used as cement, during Roman times. Pozzolan is a fine-grained pumicious material, which combines with lime to make a smooth, plaster-like cement.
Use pozzolana with lime putty in fresco painting to make hydraulic plaster for stronger fresco walls. Pozzolana reacts with slaked lime and water to form mortar with cementious properties. The fine grind (1-100 microns) of this pozzolana is best used in the scratch and brown coats of fresco. It can also be added to give "tooth" and color to grounds and paint.