Fernico

Fernico describes a family of metal alloys made primarily of iron, nickel and cobalt.

Dumet is used for a similar purpose, but is tailored for seals through soda lime and lead alkali silicate glasses.

Other metals, including copper, molybdenum, nickel, and steel can be spot-welded to the FerNiCo alloys forming low resistance electrical connections.

Given in weight % FerNiCo I has the same linear coefficient of expansion as certain types of borosilicate ("hard" glass), (c6.5 × 10−6K−1, thus serving as an ideal material for the lead-out wires or other seal structures in light bulbs and thermionic valves.

This wire is often coated with a glass-like film of sodium metaborate, (NaBO2), so the molten glass will "wet" and adhere to it.