Duty exemption for specified leather preservative imports waives excess basic duty above set rate and the additional duty. The Government exempts specified leather preservative chemicals (TCMTB, PCMC and formulations containing them) imported for use in the leather industry from basic customs duty to the extent the duty exceeds an ad valorem ceiling and from the whole of the additional duty under the customs tariff law. The concession is conditional on the importer producing a certificate from a designated officer in the Ministry of Commerce stating the description and quantity of each chemical and recommending the exemption.