Posted by Jeff in N. Texas on Thursday, May 20, 2004 at 8:10PM :
In Reply to: OT: Re-tempering cold chisel? posted by David Sherman on Thursday, May 20, 2004 at 5:27PM :
We learned how to temper chisels and whatnot in high school farm shop. We heated the chisel in a gas forge until it was red hot. Then, when we took it out, it would turn black and have a "skin", or like "slag" on the metal surface.We took a file, and cleaned off a spot where we could see fresh metal. As the metal cooled, it changed colors. I remember, that blue was too hard. The correct hardness for a chisel was a brownish tan color. When it turned that color, we dropped it into a bucket of oil or water. I do not know how scientific this is, but our old shop teacher swore by this method.