An "easy" blueing process?

[RobertD429@aol.com]

In reference to bluing metal by heat:

The gun bluing sounds like a good choice to me. Bluing by heating is a
treatment used to soften or "temper" steel to a specific hardness. I would
use it for cosmetic effect on a part under stress (like pressure bar screws)
only with due regard for its potential effect on the strength of the parts.

Steel is ANNEALED (pardon the caps; pretend they're italics) by heating to
about 600 degrees F, I think, and then slowly cooling (large castings are
often buried in sand). This makes it soft for easy bending, machining, etc.
It is HARDENED by raising its temperature again, then rapidly quenching it in
oil or water. This makes it hard, resistant to denting, and brittle. A small
amount of resilience is introduced by TEMPERING, which leaves it tough
without quite so much brittleness as the hardening. This tempering is done by
slowly raising the temperature of the metal. Different oxides form at
different temperatures (also depending on the alloy), each with a
characteristic color.

If the raising of the temperature is done carefully (not too quickly) the
color is a terrific thermometer. [Tempering is just like cooking a turkey --
if you cook it at 1000 degrees the outside will get done very quickly but the
inside will be raw.]  Anyway, the metal passes through a light straw color,
then darker straw, then very pale blue, then a couple of shades of darker
blue. Each "tempers" the hardness of the steel a greater amount, until
finally it can become too soft (like annealing).

By the way, all this has to be done particularly carefully on items of
varying or graduated thickness, like knives and chisels. It is also why
grinding a blade too enthusiastically  can ruin its ability to keep an edge
-- there is a fine line between too hard and too soft on an edge tool. The
heat of power grinding can easily soften the edge of a blade beyond the
ideal. Blades are very carefully tempered. The body of a chisel is often
treated to be softer than the edge, so it will absorb some of the shock of a
mallet. In fact, with experience, one can blue a chisel first in the fat
part, then let the heat run into the edge and just barely temper it.

Well, enough of that. As my Uncle Milton used to say, "I've already told you
more than I know."

Bob Davis, RPT