 Cold chisels come in a variety of sizes, from fine engraving tools that are tapped with very light hammers, to massive tools that are driven with sledgehammers.Cold chisels are forged to shape and hardened and tempered (to a blue colour) at the cutting edge.The head of the chisel is chamfered to slow down the formation of the mushroom shape caused by hammering and is left soft to avoid brittle fracture splintering from hammer blows.