Kooldraad

Kooldraad is a historical Dutch term for carbon-based conductors used in early electrical technology. The word combines kool, meaning coal or carbon, with draad, wire, and appears in late 19th- and early 20th-century Dutch technical writing. Because it was used by different authors to describe various carbon-containing conductors, its exact scope varied by source.

Carbonized filaments and graphite rods were produced from natural fibers or coal-tar products. Carbon conductors offer high-temperature stability and a relatively simple manufacture but are brittle and have lower electrical conductivity compared with metals such as copper. They were commonly used as resistive elements or early lamp filaments and as components in experimental devices.

With the wider adoption of copper and insulated metal wires, kooldraad usage declined. Today it survives mainly as a historical term and in niche scientific contexts, where carbon-based conductors are employed for specialized high-temperature or radiation-resistant applications.

Manufacturing historically involved pyrolysis of organic precursors (such as cellulose fibers or pitch-based materials) in oxygen-free environments to form carbonized filaments. Modern equivalents include carbon fibers and graphite conductors, which maintain some of the properties of kooldraad but with more controlled performance characteristics.

See also: carbon filament, graphite, carbon fiber, electrical resistance heating.