So Blister steel was often welded onto the cutting or striking edge of tools and weapons made primarily from reliably tough iron. Fossilized, formerly living material made up primarily of carbon. Coal contains a considerable amount of potential energy, but does not ignite easily, nor does it burn well unless fed by forced oxygen. Coal after being purified by heat at the outer edge of the fire in the forge. Coal is packed around the outside of the fire, then gradually pushed toward the center as it turns to coke.
Coke looks and feels rather like black popcorn.
An ingenious approach used by eastern Old World smiths to overcome the limitations of the materials available for blade making. The carbon content of blister steel was too unreliable to make effective tempering possible, so blister steel blades were likely to fracture in use. Iron was tough, but easily bent and blunted. Iron bodied blades with blister steel edges had to be large and heavy to make the component parts manageable. Damascus steel was made by twisting, folding, and forge welding iron and blister steel together.