I'm wanting to finish some of the things I make at home with
a black oxide type coating. It looks like the options
are Birchwood Casey, CaswellPlating and the ToolBlack
sold in Enco and others. Cold type. Any others I've missed?

Is there anyone of these better than the other?
Strong and weeks points worth considering?

We've tried some of the "cold black" systems and at best the results are
just ok, never as good as real black oxide. The last time we tried to use it
we kept getting bad "blotching" on the parts even though they were cleaned
really well so we gave up on it at that point.

Around here because of enviromental issues (California) you can't even get
black oxide treatment commercially done anymore. Its expensive, but we had
to move to "black zinc" plating. Looks good but its a lot easier to scratch
off than I would like.

For one offs, if you have a torch you should try the "heat it up and dunk it
in oil" method. Linseed oil or used motor oil are typically used, search the
web some more on these terms and you'll find some hints on using this
method. Be prepared for the oil to catch on fire if you try this, have a
cover ready to flop over the oil container.

Good luck-

Paul T.