the.com/blacksmithing

means The craft of shaping iron and steel by heating the metal in a forge and hammering it into tools, weapons, hardware, and ornament.

from Two plain Old English words fused into a trade. 'Smith' goes back to Old English 'smið,' a worker in metal, with cousins across the Germanic languages (German 'Schmied,' Old Norse 'smiðr'). The 'black' simply names the dark metals the smith works — iron and steel — as opposed to the 'whitesmith,' who finished and polished lighter metals like tin and pewter. So a blacksmith is literally the smith of the black metal, and 'blacksmithing' is just the doing of that work.