English: A cold chisel that has been frist quenched, and then differentially tempered. The blue shaft is tempered to a very springy hardness, but the edge is tempered at a very high hardness, as indicated by the tempering colors. This was done by evenly heating the entire tool, with a small propane torch, to around 350 degrees F, and then redirecting the heat to the rear end of the chisel, brushing the flame evenly across the shaft. until it turned a deep blue color. The residual heat conducted quicky to the cutting edge, so the entire tool was quenched when the edge turned the proper color. (The blue color was actually used for better photographic effect, as a chisel made this way would better be tempered to purple along the shaft, t prevent too much deformation during use.)