The peasants of a region in Germany known as the Black Forest began making clocks in the mid 17th century, but it wasn't until a hundred years later that a clockmaker added a trapdoor and a small mechanical bird to create the first cuckoo clock, reports Cecil Clutton in “Britten's Old Clocks and Watches.” Assigning a cuckoo clock to a particular year is almost impossible unless its maker happens to have signed and dated the clock; however, check for certain signs to establish a rough age for your clock.
Consider the overall shape of the clock first of all. The chalet style – in which the clock looks like a little house with a steeply pitched roof – was introduced in the 1850s. If your clock has a more boxlike appearance, then it might date to before that time.
Look next at the pendulum. Late 19th and 20th century clocks often have multiple long pendulums swinging beneath them; on earlier examples, the pendulum was short and suspended in front of the dial.
Open up the back of the clock and look at the movement. Clockmakers made the mechanical parts of the earliest cuckoo clocks almost entirely of wood. Over the 19th century, brass replaced more and more of the pieces. By the 20th century, most clocks were fitted with cheap, mass-produced metal movements, and from the 1950s onwards, manufacturers also made electrical cuckoo clocks. Because the change from wood to metal parts occurred gradually, looking at the mechanism is perhaps the best way to judge a cuckoo clock's age.
Listen to the cuckoo's mechanical "song." If its notes are strong and lusty, then the clock is probably of 20th century vintage. A frailer sound suggests that the miniature bellows that power the cukoo's song are starting to perish, which points to an earlier date of manufacture.
Check for the presence of a pungent smell of stain and oil in an apparently old clock as this smell indicates a recent reproduction or heavy restoration.
Since very few cuckoo clocks survive from before 1840, you should suspect any apparently very old examples.