Customs duty exemption for specified refractory manufacturing imports limits payable duty on certain alumina and zirconia materials. Exempts specified inputs under Chapter 28 or 38 when imported for manufacture of refractory products from customs duty in excess of the amount calculated at the rate of 55 per cent ad valorem. The Schedule lists zirconia bubbles, tubular alumina of purity 99% and above, and calcined alumina of purity 99% and above.