[jimmontg]

You said using colors to determine the temperature is a waste of time and l would tend to agree if you don't have a lot of experience heat treating. I was the HT for a machine shop and we used an oven. I got pretty good at determining the color for O1 at 1475 which is it's sweet spot. I always darken the room when forge HT so I can see the color better. Still could be off by 100 degrees which is why we have magnets, but a practiced eye will try to keep it below 1500. O1 though needs to be held at 1475 for 10-15 mins which is impossible in a forge. That hold time makes O1 an optimally better blade, but still its a decent blade with a forge HT.

But basically as you said, take it to nonmagnetic and hold for a bit longer, but of course some steels like 5160 are best taken up to 1600 so you would hold that longer still. That is why I believe there is an art factor to it when using a forge. Some steels are made for a forge it seems, like the aforementioned 5160 or 52100, 1084 and L6. I forgot about L6 as it is uncommon now, but it is great in a forge. Always look at the data sheet for a steel to determine its optimum hardening temp and then go from there and practice.