Japanese blacksmithing techniques were refined over centuries in order to create flexible, sharp swords, namely in their usage of a process of forge welding wherein unprocessed ore is interposed between steel, heated, and quickly hammered to conjoin the pieces. After being heated in a forge grate, the blade is placed into coal dust and straw ashes and annealed in a natural cooling process, though the process will also see it hardened by plunging an evenly heated, red-hot blade quickly into water. Finally, hardened blades will again be heated above the forge grate at a low temperature while keeping an eye on the color of its surface during the tempering process so that it achieves a suitable toughness. These traditional forging techniques are used to produce a wide range of Tokyo uchihamono, from those for industrial purposes to cutting instruments found around the house.