I'm definitely not an expert
but I'll toss my hat in:
I wouldn't expect black oxide on guitar hardware, as it is extremely thin and fares very poorly against corrosion without something like a constantly re-applied layer of oil to protect it.
i think the old-school hardware finishes were electroplated--probably nickel+chromate layers for chrome, gold, colored chrome flavors (chrome is literally an electroplate finish), zinc+chromate for Black. Then they started powdercoating instead, for most colors whenever possible. I believe Black is still plated.
If i'm not mistaken, this is why some colors (again, such as Black--probably zinc+black chromate), even on newer guitars, are generally notorious for holding up better than others, and why older (pre-powdercoat switch) hardware finishes are generally known to hold up better, regardless of color.
rich can correct or expound on this probably
, but based on my very limited knowledge, I suspect your guitar's hardware is black zinc plate, not powdercoat.