While looking for something else, I came across my bottle of Aluminum Black, so I just had to do this:
Looks much snappier than the originals:
Those are plain old alloy steel cap screws with a black oxide finish.
The Aluminum Black package directions tell you to apply it with a swab, rinse, and repeat, which seemed like a lot of work for a handful of pins. Instead, I poured a little into a pill bottle, dumped the pins in, and gave it a good shake to coat the pins, whereupon the cap blew off as the contents proceeded to boil merrily. A quick cold-water rinse calmed things down, with no particular harm done, although I had to chase the threads with a tap to get the black powder out. A layer of oil prettied them up nicely.
Today I Learned: the reaction between selenium dioxide and bare aluminum is strongly exothermic.
The Smell of Molten Projects in the Morning 
I mix 3gms Selenious acid + 3 gms copper sulphate + 3 cc of orthophosphoric acid in 1 Liter of water to restore blueing on my guns. Same radio of Selenious acid + nickel sulphate + nitric acid produces a blacker color. I found I am very allergic to Selenious acid crystals.
I suspect dropping the pins into a liter of solution wouldn’t produce nearly as much excitement, because the liquid would remain cooler. It might completely dissolve the aluminum, though.
A liter would blue everything in sight around here, so I’ll continue buying a little bottle every few decades. [grin]
Ed, I use a cotton bud to dab the area that needs blueing or blackening and throw away the bud. Dipping in the liter will leave a lot of crud in the bottle! I use this on iron/steel never tried on aluminum.
That’s exactly how bluing should be applied: do as they say, not as I do! [evil grin]