In the 1860’s, French clocks in slate, onyx or marble cases became popular in the United States. These cases were expensive, so the American clock manufacturers produced similar looking cases made of iron or wood. These clocks have become known to collectors as “Black Mantel Clocks”, and were popular from 1880 to 1931.
Seth Thomas made clocks in marble cases for a short time, from 1887 to ca. 1895. They also made clocks in iron cases finished in black enamel, from 1892 to ca. 1895. Seth Thomas is well known for their “Adamantine” black mantel clocks, which were made starting in 1882. Adamantine is a celluloid veneer, glued to the wood case. Adamantine veneer was made in black and white, and in colored patterns such as wood grain, onyx and marble.
Adamantine veneer was developed by the Celluloid Manufacturing Company of New York City, and was covered by U.S. Patent number 232,037, dated September 7, 1880. Seth Thomas Clock Company purchased the right to use the Adamantine veneer in 1881.
Dating the manufacture of a Seth Thomas Adamantine case is usually very simple. On the bottom of the case will be a series of numbers. For example 9881. To find the date of manufacture simply reverse these numbers to get the year 1889.