Spark-testing mystery steel for knifemaking (with Walter Sorrells video)

I follow quite a few knifemaking and blacksmithing groups on Facebook, and have learned a great deal from them. When a TTAK commenter asked a question this week about making a knife from steel from an old safe, I actually knew the answer as this is a common question I have encountered.

If one wants to make a knife from mystery metal, it is important to test whether or not at the end of all of your hard work, the material you will use will be able to be hardened to a durable edge. For this you use a spark test.

The spark patterns of different steels

From Wikipedia:

Spark testing is a method of determining the general classification of ferrous materials. It normally entails taking a piece of metal, usually scrap, and applying it to a grinding wheel in order to observe the sparks emitted.[1] These sparks can be compared to a chart or to sparks from a known test sample to determine the classification. Spark testing also can be used to sort ferrous materials, establishing the difference from one another by noting whether the spark is the same or different.

Spark testing is used because it is quick, easy, and inexpensive. Moreover, test samples do not have to be prepared in any way, so, often, a piece of scrap is used. The main disadvantage to spark testing is its inability to identify a material positively; if positive identification is required, chemical analysis must be used.[2] The spark comparison method also damages the material being tested, at least slightly.

Without a positive identification, certain steels may still be difficult to heat treat, but if one can determine an inadequate amount of carbon at the start, it will save a lot of headaches.

I am sure that there are knife-making readers who can elaborate on this. I am appreciative of anything you all have to contribute on the topic.


  1. Well done, Walter! I think that’ll help a lot. Knowing how to heat treat “mystery steels” is the next step. The method is too long to present in a comment, but I can write it up in a guest blog if there’s interest. BTW I’d love a sink made out of S30V.

    1. TheStoic says:

      I’d be very interested Mr. McWilliams sharing his knowledge!

      1. The exact heat treating of any carbon alloy steel can be determined from the steel itself. I even do this for steels I have all the tech specs sheets. First, I forge a section of a blade to a thin taper, nick it with a chisel, still hot about 1/2″ apart across the section, four cuts. Reheat in the forge-overheating the thin tip yellow orange, bright red, red, remembering the color at each nick. Remove from the fire and air cool, check for hardness with a file. If it got hard, it’s an air hardening steel, if not repeat the same heat, quenching in oil, If it got hard, it’s an oil quenching steel. If not repeat the process at the same heat,quenching in water. Forge another section as before, and chisel. Heat the section as before and quench in the determined medium. Clamp the sample in the vise at the first chisel nick and break it should snap easily, revealing coarse grain in the fractured piece. Clamp at the second mark, and snap it off. What you’re looking for at this point is the right hardness and toughness that you can hear and feel. The grain in the fractured piece should look like grey velvet-fine grey velvet-that’s the hardening temperature. To determine the tempering temperatures, make another bar the same chisel it, and heat carefully to the same color as the hardening temperature, quench and brighten up the, face of the bar with a fine grind. With a soft torch flame, bring up the temper colors from the thicker end let the colors run till the tip is light straw, med-dark straw peacock, blue. Check for hardness and toughness at different marks. Pick your hardness/toughness,

        1. TheStoic says:

          Great info. Appreciate you taking the time, that was very helpful.

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Spark-testing mystery steel for knifemaking (with Walter Sorrells video)

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