An old blacksmith's trick, used for coloring fireplace tools to
blacken and keep them from rusting, was to get some new or used motor
oil (the used oil was cheaper since you ran it through your car or
truck).  Here's an old school welder's tip (the guy was amazing but
he squeezed a nickel 'til the buffalo sh*t!):

Heat up the item until it's red hot and drip or wipe with an oil-soaked
rag until an even black color appears.  Do it outside as the smoke is
abundant and smells.

You can also use some liquids that model train people use called
"Blacken It" or "Weather It"; they have it for brass, copper and steel.
Large hobby shops carry it.  Gun shops that cater to the gunsmithing
hobby also carry bluing and blackening liquids.

Here is a web site with some interesting liquids for the art metal
crowds that will work on almost any type material.  I haven't tried
this stuff yet but it does look very interesting, for some up coming
projects:  http://www.metallicfinishes.com/

Glen R Perye Jr. - wizard works show supply