Hardening involves heating the rod to a dull red, then quenching in oil
or water according to the steel. It will be hard, but brittle as glass.
The temper needs to be reheated [drawn] to whatever hardness you want
in the finished product. Spring temper is the last stage of drawing
before complete annealment.
The old blacksmith's oxidation colors a
Light straw yellow - Gravers, burins, wood chisels
dark yellow - Cold chisels, wood chisels [heavy]
ruby red - axes, picks, impact tools
purple - heavy impact tools
blue - springs
black - soft annealed
These colors are seen on a polished area of the hardened steel as it is
reheated.
Blacksmiths hardened the points of picks, bars and chisels by quenching
[hardening] the tip of the tool, quickly polishing the end, then
letting the heat run back into the tip until the desired color
appeared, then cold quenched it. This was to leave the body of the tool
softer to handle impact.
Modern tools that you can buy over the counter are tempered much softer
so the manufacturers liability is reduced. [the tool will bend, not
break]
I retemper most of my tools. Pocket knives are especially bad today.
Bugs