A historic ironmaking process where semi-refined iron is reheated and worked on a charcoal hearth to burn off residual carbon and slag. The process consolidates the spongy mass into a dense, workable bloom of wrought iron. It was traditionally used to produce highly malleable iron for boiler plates and wire.
Heard on the job
They used to knobble the scrap iron with charcoal to get the purest wrought iron for the boiler tubes.