This little antique thimble case is carved of ivory in the form of an acorn and is engraved with patterns of Madras work dots and circles on the top and around the sides. This is a form of scrimshaw work where black lacquer was flowed into the engraved designs.
It unscrews and inside is a tiny silver metal thimble. It's about an American child's size 0-1 (10.6 mm in diameter). It's in great condition with no holes, dents or damage.
Except for a little rubbing, the condition of the acorn is excellent. It measures 7/8" high and 3/4" in diameter. A variety of Madras work needlework tools are shown on p. 87 of Nerylla Taunton's book "Antique Needlework Tools and Embroideries".