other things that 'tools are also given a harder tempering in the urine of a small, red-headed boy than in ordinary water'. One of the fuller early discussions of quenching is the first Western printed book on metallurgy, Von Stahel und Eysen, published in 1532, which is characteristic of late-medieval technical treatises. Modern scientific study of quenching began to gain real momentum from the seventeenth century, with a major step being the observation-led discussion by Giambattista della Porta in his 1558 Magia Naturalis. Mechanism of heat removal during quenching Heat is removed in three particular stages: Stage A: Vapor bubbles formed over metal and starts cooling During this stage, due to the Leidenfrost effect, the object is fully surrounded by vapor which insulates it from the rest of the liquid. Stage B: Vapor-transport cooling Once the temperature has dropped enough, the vapor layer will destabilize and the liquid will be able to fully contact the object and heat will be removed much more quickly. Stage C: Liquid cooling This stage occurs when the temperature of the object is below the boiling point of the liquid. See also Quench press Tempering Martempering Austempering Hardening_(metallurgy) References External links Metal heat treatments