First, I clayed up the four tantos I feel were not successful, and tossed them in the oven to cure for an hour. While they were curing, I turned the heat treat oven to full on, and raised the temperature to 2000, and held it there while the tantos cured. This got the whole of the oven, heavy refractory and all, up to a fairly even temperature.
After about 45 mintues, I turned off the burners and let the oven slowly cool down with all ports blocked for the remainder of the hour. At the end of the hour, I removed the tantos from the curing oven (ok, it's my kitchen oven) and took them out to the forge. The heat treat oven was at about 1800 deg, a bit hot, so I opened the door and let it cool down to 1600 or so. Since the thermocouple is in a relatively exposed position, it cooled down faster than the rest of the oven with the door open, which works fine for me, as the relatively cool tantos will suck heat out of the oven.
Anyway, once the tantos were in the oven, sure enough the temperature rapidly rose to 1650 degrees F -- a bit hot, but it was soon dropping fairly rapidly even with the doors closed. After about 5 minutes, the temperature hit 1550, and I turned the burners onto minimum, which is just about right for keeping the temperature stable (it actually drops about a degree a minute.) I then walked away for half an hour, mostly so I wouldn't keep opening the door to check on things and mess up the temperature.
After watching "Most Extreme Elimination," a truly bizzare show on TNN, I headed back out. The temperature was at 1502, almost perfect. The tantos were, as far as I can tell, at an even temperature, glowing at about the same intensity all along the lengths of the blades.
One after another I quickly quenched them in water. Once they stopped hissing, meaning that they had dropped below boiling even under the clay, I pulled them out and took a look. All four quenched without cracking, without warping, and a file check showed that they had all hardened! One of the key indicators of a good quench that I've noticed in the past as well is that the clay coat stayed on until after the blade had cooled, but it fell off readily once the blade was removed from the quench -- and this happened with all four blades.
The blades are back in my kitchen, undergoing tempering -- although traditional blades are not tempered, I temper mine to a low temp, 350 F, to relieve stresses from forging and heattreat. Since the blades are higher carbon and uniform consistency, unlike traditional blades, I feel this produces a better knife, while the low tempering temperature keeps the hamon bright and visible.
Tomorrow I'll start polishing and see how the hamons came out. I do so hope that this time they work out well.