Easy black armour recipe.

-Prime whatever, in your case black. - Corvus Black layer (you want a black base you can touch up and you cant do that on flat primer) - take a thin brush a carefully wash all those spicy tau details with nuln oil (if you have some that brushes over onto your armour plating that's fine you can touch it up after with a little Corvus if need be) - edge highlight eshin grey (this is your main highlight keep it thin but pretty well over all coverage) - dawnstone edge highlight (this is where less starts to equal more you want this on the most pronounced edges where the light hits it most) - admin. grey edge highlight (this one is minimal like small dots or on corners just to show a point of light)

Any of these blend together fairly well for smooth transitions as well if you don't like the above given gradient.