Hand Tools

Re: Oven tempering
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Steve Voigt
I bake in a kitchen oven, with about the same indulgence in details as you all planing. In my experience there is nothing uniform either spatial or temporal about any place in any oven I have baked in. And if the oven is electric, radiant heating becomes significant which in turn means IR absorption/reflection of the metal becomes significant. (dark bread pans bake faster than shiny).

I agree with all this, Bill. If you put a piece of bare steel on the rack and heat it to say 400°, you are likely to get a rainbow: gold, brown, purple, even blue if you're unlucky.

Here's how to temper accurately in an oven. You'll enjoy this if you're a baker.

First, get an insulated cookie sheet. It has to be insulated, not just any sheet. Cuz duh, it insulates. Put it on the top rack.

Second, put a heavy cast iron pan (or two) on the bottom rack. This'll act as a heat sink.

Third, always preheat the oven before you put your steel in. Good practice when baking too, right?

Last, you'll need to calibrate the oven thermometer, since it obviously may not be correct. You can use an external, accurate thermometer, but it's not necessary--trial and error will work fine. Start at 300° and work your way up. Make sure you use a piece of clean, bare steel (preferably O1 or other HC steel) when calibrating. At around 375, you should see a light straw. 400 is a nice gold color, and so on.

It's important to judge color out of the oven. Put the steel on a white plate or sheet of paper (after it's cool, lol). It's really hard to read color accurately in the oven or on a dark or metallic background like the cookie sheet.

I just read Dave's description of how he tempers. He's obviously got a process that works for him (using a specific spot in the oven) but it may not be replicable. Probably can't do batches, either. I sometimes do a dozen irons at a time, and they all come out the same gold color (or they would if I abraded them all before tempering; the process is so dependable that I no longer do that--I just throw them in the oven after HT, and clean them up afterwards).

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