Fair question badgerknives. Plate quenching essentially is another way of quenching steels that will quench in still or blown air. Examples would be all (I think) of the CPM blade steels - common stainless steels like ATS34, 154CM, 440C, 19C27, Elmax.... the are many dozens. When the blade comes out of the kiln (or well controlled forge) after it's soak in a tightly sealed foil envelope, we used to take the blade out of the foil to cool in air, or in front of a fan. People are now leaving it in the foil and placing the packet between thick plates - usually aluminum. This cools the blade quicker - even with minimum contact, but very importantly, it ensures the hot blade never sees oxygen - so it stays relatively clean and shiny. Generally, a point more hardness can be acheived compared to air quench as well. Cheap - Easy - Now widely accepted - and it saves a whole load of clean-up after heat treat. Anyone who can heat treat air quench steels can do it easily.