An "easy" blueing process?

[David Parkhurst]

Thanks to all who offered solutions to my query concerning the
blueing of pressure bar screws. I tried a number of the
suggested techniques but eventually settled on one which I don't
believe was mentioned, yet produced the richest and deepest and
blackest blue -- without a hint of brown -- and so I'd like to
offer a report:

I simply heated the polished and superclean screws carefully in
the flame of a propane torch (any clean heat source would do)
until the temper colors showed in the shade I desired and then I
dipped them immediately in cool water and dried them off.

The tricky part (art?) is learning to control the application of
heat and judging when to stop. Careful and uniform polishing
before heating proved to be essential and the finest finish
yielded the deepest and purest colors. The hue (assuming uniform
polishing) is directly determined by the temperature to which
the steel is raised -- not by the length of time it is exposed
to that temperature.  As the temperature rises the color (a
product of oxidation) changes through a very predictable
spectrum. The first color to show (at the lowest heat) is a
light straw which progresses to a dark straw and then on
through several interesting shades until purple is reached, then
blue, then peacock and finally the coloring returns to plain
steel. Any increase in temperature beyond this will begin to
produce incandescent coloring and may affect the crystalline
structure of the steel.

Ideally, all the prepared screws would be placed together in a
heat-treating oven and carefully heated to exactly the same
temperature, thus ensuring the greatest uniformity.
Nevertheless, I found that with careful manipulation and a
little practice I was able to acheive reasonable consistency.

I held each screw by means of a six inch piece of iron wire
coiled a bit at one end so as to wrap around the threaded
portion and engage a few threads. I formed the rest of the wire
to be straight and hold the screw's axis in line with the
wire's axis, thus I could rotate the screw by rotating the
wire. This made it easy to control the heating.

One nice aspect of this method is it's easy reversibility: if
you overdo it just repolish the screw, removing the offending
colors, and reheat again.

This method will only work on steel.