Bidri is a brass alloy, which contains zinc, copper, lead, tin and traces of iron. After making the surface smooth, a solution of copper sulphate is applied to the Bidri Ware to darken it temporarity for engraving. The engraving tools cut the intricate but delicate tapestry of design into the metal, which is then lighter in colour. Each piece is then handed over to the inlayer. The inlay may be of silver, brass or gold. The surface of the decoration blackens after the inlay has been burnished. This is done by applying a paste of ammonium chloride, potassium nitrate, sodium chloride, copper sulphate and mud which darkens the body by producing a characteristic black patina, but without damaging the inlay.