For painting black you would actually highlight to a lighter color leaving only the pure black for the shadows
If you wanted to do washes, that would mean staring with a color that is dark but not black, then you could do black washes
Personally I prefer highlighting up from black. Looks like you started to do that already with some of the edges
So starting with a black base coat, basically mix either some brown, blue, or grey into your black so you have something that very dark without being black, then go an paint over all but the deep recesses with that color
That is the process I used for the Alien Queen and Alien below
I primed Black. Then used Army Painter Sith Robes (which is more like greyish black with a hint of brown seen here in the third row down in this color sample
I painted all but the deepest recesses that were to remain shadow like
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I mixed in a bit of grey and brown to that and did some of the higher parts
then I also did a drybrush with white/grey/brown mix of oils since it was easy to blend which basically hit things like the edges of the plating etc...
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And here I did a similar thing but stuck with all acrylics and shifted it more grey and blue than brown for a different tone
start from black, add more blue and white was highlights increase
at normal viewing distance something like this
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zoomed way in to show the exaggerated contrast you can see it is actually mostly a blue black with highlights with only pure black being in the undercuts and creases
If you go to light in your highlighting you can then do a straight black wash to tone it down a bit
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Hopefully that helps?