Hank Rearden
I was reading about a smith who holds the heat to temper steel at 400 degrees for and hour and I wasn't sure how to know your doing that consistently over time. The obvious answer is a pyrometer. Do you have to monitor the entire process every few minutes? Or do you use the color of the steel?

I sure could use some help here.
code[Maglio.gif]  Keep the fires burning hot!
2020 ABANA Conference in Sarasota New York. June 3rd. through June 6th. Plan now!
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anvil
how to heat treat by eye and be within ~50 degrees

Better late than never!

Your can learn to do this "by hammer in hand" and be within the tolerance of error both of the steel specs and any electrical ht tools you may want to purchase with about a years worth of due diligence.

This applies to a coal forge and a hand crank blower. Any blower works if you can control air flow.

The most critical "must do" is to have your forge in an area where you have constant light.

Next you need to have a color chart like you posted and the one I added with celcius. Make a copy of it, laminate it and hang it by your forge within handy reach.

Get in the habit of looking at this often whilst raising/lowering the temp of your steel and associating the color of your iron to the colors/temps on the chart.

Consider this very similar to learning scales on your guitar! The more you practice, the better you will be. Notice that the forging temps are ~100 degree increments. The temper colors are all defined by specific colors as well! Remember, these colors, under a constant light represent constant temps no matter your steel or its thickness. If you do this, depending on your "due diligence", you should be pretty proficient within a year at associating colors to temp within ~100 degrees! Also note that the range given in the specs for your steel usually fall within this range as well.

Also note that all electronics equipment have a coeefficient of error. The cheaper the tool, the larger and may not even be listed in your tools specs. A very quick survey I did a few years ago showed me that in many tools under 10 grand had a coeefficient of error of ~+/- 10%. This means when your Gage says you are at 1500 degrees, your accuracy is within 1350-1650. Your mark one eyeball tops this already! Practice with your individual electronics tool allows you to be closer. Same with yer eye. All things considered, within this price range eye and electronics are close.

So now you can identify temps by color and be within specs. Not bad for a year!

Next and on to your question plus refining your eyeball! Consider this learning new guitar licks and embellishments.

During this year pay close attention to finding the heating sweetspot for all cross sections you deal with.

Sweetspot? WTF??? Well, that's fire control. The sweetspot is how fast you increase the temp of your piece no matter its cross section so that the color you see on the outside matches the temp in the center of your piece. Too slow and you waste time. Too fast and you have an uneven heat. This translates to how many revs on your hand crank per given time and cross sectional thickness. Hey, it takes longer to heat up a 1" square than it does a 1/4"*1* piece! The sweetspot stays the same, time changes.

Once you have a handle on this, your skills are pretty proficient. And all eadily within that year of due diligence. Now for the new licks!

Accuracy: now its pretty easy to know how many revs it takes to raise your work from one color to another,, about 100 degrees. Divide that in half and you are within the ball park of being within 50 degrees(+/- 25 degrees).

Soak time: now that you know how many revs in a given time it takes to reach any color(temp), you can easily figure out how much you need to back off to maintain that particular color(temp) to the above tolerance.

Set the timer for whatever time called for,,, wait for the ding,,, and you are right on the money!

Done within a year or so! Now for the rest of your blacksmith life, all you can do is get better!

Enjoy
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Hank Rearden
Bang! Anvil you have touched on some very interesting skills. Some of these have developed without any cognitive thought on my part. I guess it's been somewhat organic for me. Soak time is what I recognize I've managed on my own with out thought. It seems I'm pulling my iron out at a consistent color during the past few sessions. Meanwhile I'm doing other task to prepare for the next hammer strike. Example, brushing scale from the anvil, choosing the next hammer or hardy, cranking the blower etc...

Now that your post has brought up variables to pay attention to during heating I'll work on identifying temperatures I'm actually working with.

I forge outside often and until I get a permanent building seeing the colors has been a plague. That may be the reason my since of timing is more acute.

JMCCUSTOMKNIVES was the first to tell me about the problems of the sunlight identifying forge temperatures for steels that have a narrow workable temp range.
I stayed with mild steel since I haven't ruined any steel forward.

The movement of the Sun across the sky has been the devil.

I will be making adjustments from here forward. Thanks for the post.
code[Maglio.gif]  Keep the fires burning hot!
2020 ABANA Conference in Sarasota New York. June 3rd. through June 6th. Plan now!
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anvil
You can learn to read colors in any light. However it is a magnitude harder if you try in changing light.

If you learn to read colors in a constant light, it is much easier to learn to read them in daylight.

It always draws a Crowd at a demo when you do a forge weld.
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