I acquired a set of Gensco chisels with yellow plastic handles a while back. All of the chisels except for one were in pretty good condition.
The chisel that was in poor condition looked very rough. The blade was rusty, covered in gobs of glue, and bent near the middle. Fortunately, the handle was still in good condition.
I cleaned off all of the glue and rust by scraping and sanding. When done, I noticed that the bend in the blade was about half-way up … in an area that I assumed was hardened and tempered. I was curious so I mixed up a little batch of citric acid and water (8 parts water to each 1 part of citric acid) to try to find the blade quench line. I wanted to do this before I finished shining up the blade.
The quench line showed up clearly, just about half way up the beveled portion of the blade. The line was tilted downward a bit from the left side to the right side, making me wonder about the quenching process used at the Eskilstunasteel factory.
The bend in the blade was just above the quench line, which makes sense; the steel was softer there. I put the blade on my steel anvil and carefully straightened it with a few hammer pounds.
The reason that citric acid shows the quench line is because it reacts differently with the hardened and the unhardened steel.