Boron trioxide

Boron trioxide, B₂O₃, is a compound of boron and oxygen. It is usually seen as a colorless, glassy solid, because it is a glass former itself: like silica, its atoms link into a random network rather than a neat crystal.

Its boron comes from minerals such as borax and colemanite, mined in a few places, notably Turkey and California, where it is already bonded to oxygen. These are processed into boric acid, and heating boric acid drives off water and leaves boron trioxide. Glassmakers often add boric acid or a boron mineral to the batch directly and let the furnace do the rest.

In glass it does two jobs at once. It lowers the melting temperature, so the batch melts more easily, and it makes the finished glass expand less when heated, so it is less likely to crack from sudden temperature changes. That is the secret of borosilicate glass, used for lab and oven glassware. In the TV, boron trioxide goes into display glass, whose low expansion keeps the panel's tiny patterns aligned as it heats up, and into the E-glass of glass fiber used in circuit boards.