I posted the sodium theosulphate method here many years ago. The full
instructions may still be in the FAQ. Make sure the items to be blackened
are fully degreased.

Steve R.


"George" wrote in message
...
"Pedroman" wrote:

I need to coat steel parts (small) with a black oxide coating but in
small
lots. Parts are 3 1/2" X .75" and are basicly steel stock with drilled
holes
for alignment pins. Anyone have a small shop style setup that could share
info on the process. I'm currently having someone else do it but at $50
minimum I have to build a lot more than I use in a couple of months to
make
it worthwhile. Sometimes I go through 100 in a month and sometimes 500 it
just depends. Stocking 1000s of this item is not really worth it unless
that's the only route I can find.

A friend commented that a used commercial french frier would be about the
size I would need and it certainly can generate the heat required. I've
checked around and those things are cheap to find.

Anyone?
Pedroman

One method that I have used with some success is a pot of hot Sodium
Thiosulfate, more commonly known as Photographic Hypo. Make sure that
the parts are thoroughly clean and dip them in a solution of hot water
and hypo. It depends upon the material that you are coating. This can
produce anything from a crummy brownish smudge to a fairly attractive
bluing to a rich black coat.

For a more fool proof (and more expensive) solution get some of this
stuff:

http://www.eastwoodco.com/itemdy00.asp?T1=10113+Z&I1.x=40&I1.y=38

From Eastwood. The advantages are that this is a cold process and the
chemicals can sit on the shelf almost indefinitely. If there is a
disadvantage it's the fact that as the stuff comes to the end of its
life, it leaves a splotchy coating that is a PITA to correct.

George.