[SEL] bolt/fastener finishes

[bill at antique-engines.com]

I've got a project going that has bolts, nuts and washers that aren't
"zinc" or "galvanized". They are black. Best I can tell is they are zinc
phosphate (not phosphate and oil)
They actually held up as well as if not better than the silver plated
bolts and nuts in the same areas.
I'd like to get the SAME look - the flat black of the zinc-phosphate and
not use the silver/zinc plated bolts.
Some are special - flange nuts, thick washers, etc.
Is there a way I can do this at home?
Please don't suggest paint - paint chips when you wrench and adjust things.

I have a plating kit and the silver colored bolts and such that you can't
get at a hardware store I use electrolysis, media blast, soak in Fast Etch
(removes remaining rust and leaves a phosphate coating) then tin/zinc
plate them. They turn out like new except for the roughness from rust
pitting in areas.

In short, looking for a good way to restore the flat black look of zinc
phosphate bolt and nut and washer finishes.

Bill

(My next project - redo a maytag twin I have with black krinkle
powdercoating!)