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By repeating and testing, and paying attention.
My first attempts at HT were hit and miss. That's normal.
That is why you have to look at the colors before quenching, look at the steel after...

+1

I don't want to discourage anyone from the scientific approach. Science is good.
However, smiths have created absolutely fabulous blades for centuries by eyeballing the color.
In fact, smiths...

Since the temperature already correlates directly to the temperature of the steel, isn't thermal paint a bit redundant?
It's O1 we're talking about here, which is very easy and forgiving in heat...

You say 1/6" steel?
How wide do you make your razor? The minimum ratio for thickness vs width is 1/4. Go below that and you will get problems with your edges.
For 1/6" steel, this means the maximum...