How to blacken rear sight (permanently)?

[hunterbench]

The old Michigan armament I've been shooting shot quite low so I removed the wilson combat rear sight after a friend offered to have the local saw mill machine shop silver solder an extension on top of it. They did a great job. Looks like they're shooters. It came back complete with bead blasting and perfect milling. It looks good. It is also shiny enough to shave in.
Besides sight black what can be done to permanently make this dull black?

[Armorer]

If it's not aluminum, try Oxphoblue by brownells. Good stuff-- far better than anything Birchwood Casey's makes. Try wrapping a bit of 000 steelwool around a Q-tip and buffing that in-- it'll turn almost a dull chrome-bluish color like a well worn Colt.
Dab on some clear lacquer or nail polish, an extra fine coat.
Air dry a good hour and then take a rubber eraser with some more 000 steelwool wrapped thinly over it to just give it a few strokes.