The base company for Seth Thomas.
Seth Thomas was born in Wolcott, CT in 1785, went to work for clockmaker Eli Terry in 1807, bought out Terry’s factory (together with Silas Hoadley) in 1810, and in Dec. 1813 bought out Heman Clark’s clockmaking business in Plymouth Hollow.
Thomas continued Clark’s wooden movement tall clock production, and about 1817 began making the wooden movement shelf clock. These were cased in pillar and scroll cases until 1830, when the bronze looking glass and other styles became popular. In 1842, brass movements were introduced, and first cased in the popular O.G. case (which was made until 1913). Wood movements were phased out in 1845. In 1853 Mr. Thomas incorporated the Seth Thomas Clock Company, so that the business would outlive him. Mr. Thomas died in 1859, and Plymouth Hollow was renamed Thomaston in his honor in 1865.
Mr. Thomas was very conservative, and after his death many new styles of clocks were introduced by his sons. Regulator clocks were introduced in 1860. The patterns and machinery for these had been purchased in 1859 from the creditors of bankrupt clockmaker Silas B. Terry. Spring driven clocks were introduced ca. 1855–1860. Perpetual calendar clocks were made from ca. 1863–1917. Some of the most popular later types include walnut kitchen clocks, made from 1884–1909; marble clocks, 1887–ca. 1895; black (Adamantine finish) wood mantel clocks, ca. 1885–1917; black enameled iron cased clocks, 1892–ca. 1895; oak kitchen clocks, 1890–ca. 1915; tambour clocks, introduced in 1904; chime clocks, introduced in 1909; and electric A/C clocks, introduced in 1928.
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.
References: The above summary was adapted from Chris H. Bailey’s writings in American Clock & Watch Museum reprints of American clock catalogs, and in History, Identification & Price Guides by Tran Duy Ly. Mr. Bailey is the horologist at the American Clock and Watch Museum in Bristol, CT and has done a superb job of compiling information about many American clock companies. His writings are highly recommended to anyone who wants more detail than has been given here.