BERYLLIUM

Beryllium is the chemical element with atomic number 4 and the symbol Be. It is a lightweight metal with a light grey appearance. It was long valued in watchmaking for its ability to harden alloys and, most notably, for its very low coefficient of thermal expansion. Beryllium is found in steel alloys used for manufacturing balance springs (such as Invar and Elinvar), in Glucydur — developed for making balance wheels — and in beryllium bronzes (used for balance wheels, endstones, etc.).

As a toxic substance, beryllium is now subject to REACH regulations, and considerable research is underway to find suitable alternatives.

Useful links:
– Balance spring
– Balance wheel