Slagging

Slagging is a term with multiple meanings depending on context. In metallurgy, slagging refers to the management of slag, the non-metallic by-product formed when ores are smelted or refined. In British English informal speech, slagging or slagging off denotes harsh criticism or insults directed at someone.

In metallurgical practice, slag forms when fluxes such as lime or silica react with impurities in the molten metal to create a layer rich in oxides. Because slag is typically less dense than the metal, it floats on the surface or forms a separate tap-able layer. Slag serves several roles: it collects impurities, protects the molten metal from oxidation, and helps regulate furnace chemistry and viscosity. Common ferrous slags include blast furnace slag and basic oxygen furnace slag; non-ferrous slags include copper slag and zinc slag. After processing, slag can be used as a cementitious additive, an aggregate for road construction, or in the production of mineral wool and other materials. Environmental considerations focus on potential heavy-metal leaching and the management of slag dumps or landfills.

In language use, slagging off means to criticize or disparage someone, often in a direct or public manner. It is informal and regional (notably in the United Kingdom and Ireland) and can be considered rude or offensive in formal or professional settings. The term derives from slang for a person regarded as worthless and has extended to mean verbal denigration.

See also: slag (by-product), slag cement.