BERYLLIUM

Beryllium is a light alkaline-earth metal (atomic number 4, symbol Be, density 1.85), rigid and steel-gray in color, which exhibits a high modulus ofElasticity and remarkable fatigue resistance. In watchmaking, it is practically never used in pure form, but as a copper-beryllium alloy (CuBe, or beryllium bronze), hardenable by precipitation heat treatment. This alloy has notably been used to make Click springs, plugs, winding stems, and Balances high-inertia monometallic alloys — such as Glucydur, a CuBe alloy with added iron, whose very low coefficient of thermal expansion precisely spares the balance from a bimetallic compensation device. Non-magnetic and corrosion-resistant, CuBe combines dimensional stability with good thermal conductivity. Its use, however, remains strictly regulated: beryllium dust and fumes are highly toxic and classified as carcinogenic, requiring enhanced respiratory protection during the machining or Polishing of the parts made from it. Many manufactures have since replaced this alloy with less hazardous solutions, such as Brass or special steels.