In general, you are not allowed to use ivory and materials stemming from endangered species commercially. An exception has been made for “antiques”, crafted before 1st June 1947.
Antiques are unmodified artefacts. Raw materials that still can be turned into an artefact, like for instance a tusk of an elephant or a raw rhino horn are excluded from legal trade, as no proof can be given that they already existed before 1947. Reworked ivory, like snooker balls that were turned into umbrella handles after 1947, are equally not allowed in commercial trade.
Since all miniature portraits here presented, including their frames, have been made long before 1947 and have not been reworked or turned into another object ever since, their trade and commercial use is completely free under the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).
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