Glucydur is a trademarked beryllium bronze, made of beryllium, copper and iron, used for balance wheels and other parts in mechanical watches. It is hard, resists magnetism and keeps its shape. That stability lets a balance be poised at the factory and stay in poise for the life of the watch.
Why is Glucydur used for balance wheels?
The alloy has a Brinell hardness of about 400. It also resists magnetism and deformation. Those qualities suit precision parts that have to hold their exact dimensions, and the balance wheel is one of them. A Glucydur balance does not drift out of shape over time. That is why it can be poised once at the factory, with its weight evenly spread around the wheel, and then stay in poise for as long as the watch runs.
How is a Glucydur balance different from older balances?
Older compensating balances carried screws around the rim. These screws were part of how the balance dealt with changes in temperature. A Glucydur balance needs no rim screws. The alloys used in today’s balance springs handle temperature correction instead, so the wheel itself can be a plain, smooth ring. Most high-grade modern wristwatches use a smooth, screwless balance of this kind.
Where it comes from
Glucydur is based on beryllium copper, which two German metallurgists, Georg Masing and Otto Dahl, invented in the 1920s. With heat treatment, beryllium copper can become about as strong and hard as alloy steels. Glucydur was developed in the 1930s, in parallel with Nivarox, an alloy used for balance springs. Glucydur balances paired with Nivarox springs soon came to dominate the watch market. The company Glucydur moved to Bienne in 1970 and was reorganised as Glucydur AG in 1973.
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