Rhode Island Commercial & Illustrated Mail
William K. Potter - Shell Goods Manufacturer - 1895

The horny, translucent mottled substance, obtained from the backs of certain species of turtles, was widely used, from the mid-18th century to the early 20th century in the manufacture  of combs and hairpins. It was noted for its warm mottled colors which were often further enhanced by silver.

The advertisement is on the back of a Penny Postcard - Scott #UX12 issued on January 2, 1894