Customs exemption for non optically worked optical glass caps payable duty at a specified ad valorem rate upon importation. Exempts imports of optical glass and elements thereof that are not optically worked, falling in Chapter 70 of the Customs Tariff, from customs duty to the extent that such duty exceeds an amount calculated at a capped ad valorem rate; issued under Section 25(1) of the Customs Act and given an effective commencement date.