Thread: The Shadows in the Steel

For those of us doing our own heat treatment (and often with less than professional equipment), judging the correct temperature of the steel before quenching is of paramount importance and, sadly, is very hard to judge with much accuracy. This is meant to be a "short" story with an observation that might help someone who wants to get in on the fun we call razorsmithing.

My general smithing procedure is to start with a piece of barstock that has been approximated as being large enough to make the finished tool, heat it up and begin hammering out what looks like a razor. Once it is acceptably close to the final desired shape, I move on to the normalizing/heat treating steps and so begins the need for accurate temperature gauging.

The magnet test worked on many occassions and I felt very comfortable in using it. But after having two or three blades in a row turn out surprisingly mediocre because of the slight margin between the tempertaure that iron loses it's magnetism and the actual austenitizing temp for the given steel (insert "I told you so's" here), I went looking for better options.

So I picked up a digital pyrometer that will read temperatures far beyond what I ever intend to use it for from Auber Instruments. It's quite nice to have an actual number to put on that blazing orange glow in front of you, but I couldn't help notice that there were inherent hot spots as well as cold spots at various points throughout the interior of the forge. I figured that if the pyrometer was reading close enough to the steel that the temperature would be accurate, and for the most part, it is.

All the while, in the back of my mind I'd been trying to watch for "the Shadows" that supposedly dance across the steel when the critical temp is reached, but to no avail. I just couldn't discern the shadows while the steel was in the forge and this was rather unsettling because the shadows verify without doubt that the steel is ready to be quenched.

But then came the realization that the shadows don't necessarily have to be seen directly; I could watch the rate that the steel heats up at, watch for it to slow down, then when it starts to pick back up the critical point has been crossed. Maybe it's just my eyes, but for whatever reason, it's easier to see the steel go from black to faint dull red, to dull red, to red, then stop for a short period of time then go to red orange (which is the decalescent point being surpassed) than it is to see shadows moving across the blade. Maybe if I were making larger blades it might be easier to see some parts transitioning while others are still heating up, but for my forge and the small size of the razor, I just can't see the little buggers.

So for those who want to give this whole thing a shot, watch for how fast the steel goes through the color changes, try to spot the inconsistency and you will have seen "the Shadows in the Steel".

It's easier to see the changes in DE-calescence than re-calescence. And like so many other subjective judgements, color gradients etc., this one takes on the character of riding a bicycle. Everybody finds their own style and everyone learns to balance eventually.

I can't argue with, and can only support, the idea that knowing what the temperature is objectively will help improve everything. But I can't disagree with not spending money when your eye and human computer can be very effective without the technology. Training the computer will take only time and experience. Subtleties are difficult at best.

One thing I'd ask folks to consider is the requirement for a "blazing orange fire." My tradition has come out of the school of a bigger fire is always better. Until a few years ago when I began experimenting with venturi burners, I didn't realize that sometimes a small fire can be a very good alternative. This type of forge is exceptionally controllable and with a good ear (surprisingly like a musical instrument) the fire tells me when it's right. After multiple confirmations with the skeptic's thermocouple, I can get this little forge to ride along pretty much where I want it for austenitizing temperature. This allows for a reasonable soak time without worrying about overshooting the temperature in an "on or off" kind of fire.

It's a fascinating pursuit of how the steel and the tools both contribute to learning. Observation is the key. You can't avoid it.

Thanks Mike!

I've noticed that the different types of atmosphere change how the steel heats as well. It seems like a fuel rich atmosphere heats more evenly than when it's lean, and that color of the fire changes with that ratio as well. For most Austenitizing heats the forge is more of a deep red, just so that it's harder to over heat the steel before the quench.

Half of the enjoyment with this whole thing is learning just how fluid a process it really is, much more flexibility and variation than you realize when starting out.

"Observation is the key. You can't avoid it."

I like that, it's too true.

i love watching the "dance" but then again i can crack the kiln door open to see that and to make sure i have a good even heating on the blade