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.
The movement provides a guide to the date of an Adamantine clock. At first, most Adamantine clocks used a modified shelf clock movement (called the “hip” movement because of its shape) with the escapement outside the back plate. Around 1900, the model 89 movement was introduced, having the escapement between the plates. The two types can be distinguished from the front of the clock by the position of the regulating square. The back escapement type (up to ca. 1901*) has the regulating square above the numeral “12”. The model 89 has the regulating square below the center of the dial. These two types are evident in the illustrations above.
Many Seth Thomas clocks from 1881 to 1918 have a date code stamped in ink on the case back or bottom. Usually, the year is done in reverse, followed by a letter A - L representing the month. For example, April 1897 would appear as 7981 D. THE CLOCK MEASURES APPROX 16 INCHES WIDE BY 12 INCHES TALL BY 6 INCHES DEEP.