Longcase clocks, most commonly known as “grandfather clocks” are weigh-driven, pendulum clock mechanisms housed in tall wooden cabinets. Typically, the cases are elaborately ornamented with carvings on the crown, where the clock face is housed.
English clockmaker William Clement is credited for developing the long pedulum mechanism in 1670. These mechanisms kept better time than earlier designs but required taller cases to fit. Thus the longcase clock was born. The design was further improved by George Graham in 1721 who compensated for the temperature changes in the pendulums, by placing mercury in them. This made the clocks accurate to 1 second a day.
As a general guideline, longcase clocks over 6′ tall are considered to be grandfather clocks, clocks between 5’4″ and 6′ are considered grandmother clocks, cased clocks under 5’2″are classified as granddaughter clocks. There are other considerations such as hood ornamentation, case width and shape which may also factor into the classification of the clock, but height is normally the most important factor.
When it comes to identifying genuine antique loncase clocks, there are two main recognised types: the Comtoise grandfather clock and the Bornholm grandfather clock.
The Comtoise clock (also known as Morbier or Morez clocks in Europe) gets its name from the Franche-Comte region of France, where it started production from 1680 and continued for approximately 230 years. This variety was popular in France and other parts of Europe, including Germany and Spain. Key feature of the Comtoise clock is the curved “violin shape” of the lower side of the pendulum case, the pedulum itself is protected by a heavily decorated wooden sheath.
The Bornholmeure clock comes from the Danish island of Bornholm, where it was manufactured between 1745 and 1900. The case is characterised by its elongated, rectangular form and closed cabinet compartment for the pendulum (as opposed to a glass window to show the inner workings of the clock). The origins of the design stem from a Dutch sailing ship which ran aground onto the island in 1744. Among other cargo, the ship carried five grandfather clocks from England. A local turner managed to repair the damaged clocks and started manufacturing the clocks himself. Although popular initially, the clock production all but halted by the end of the 19th Century.
Antique longcase clock mechanisms can also be categorised as either 30-hour or 8-day types.
A 30-hour clock does not require to be wound by key, as it uses a weight and chain mechanism to wind itself. This variety was cheaper to produce, consequently making it less valuable.
The 8-day clock had to be physically wound once a week, with a mechanism that allowed for an extra day, in case the owner forgot to wind it.