Seth Thomas wall clocks enjoy a history that began in 1810 when Seth Thomas bought Eli Terry's factory through today and the Alliance Time Company, which acquired the entire inventory in 2009. Dating a Seth Thomas wall clock is a lesson in time itself.
Examine the clock for signatures and/or dates on the dial or workings. The back of the clock may be removable. If so, use the magnifying glass to look over the inner movements, also.
Note any times, dates, places of workmanship and any other information gained from looking over the clock. Some older Seth Thomas clockworks are wooden. Wooden clockworks would date the clock between 1817 and 1830. In 1830, the company began to use brass movements. Wood movements were no longer in use after 1845.
Study your history. The Seth Thomas family business introduced regulator clocks in 1860, and spring-driven clocks between 1855 and1860. Between 1863 and 1970, the company produced perpetual clocks. Between 1881 and 1918, most Seth Thomas clocks were stamped in ink with codes on the bottom or on the case back. Note that many Seth Thomas clocks were reverse date stamped with the year and then a letter for the month of production.
Be aware that some Seth Thomas clocks are not marked. In these cases there may at least be a paper label that will tell you the name of the manufacturer, where the clock was produced and the date of manufacture. Unfortunately, these labels may not be intact enough to gain additional information.
Identify some Seth Thomas clocks that are neither marked nor have paper labels by being familiar with the styles of clocks. Styles have changed over the years and will aid in determining the time frame in which the clock was made. Use a good book, either purchased or from a library, to match time frames of clocks with styles and makers.