Atramentum Black vs Blue Wash

How close are they?

ΔE 47.1, loose: different enough that you should pick on purpose. Blue Wash is noticeably lighter, much more saturated than Atramentum Black.

Can I use Blue Wash instead of Atramentum Black?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 47). Blue Wash is noticeably lighter, much more saturated than Atramentum Black.

Can I use Atramentum Black instead of Blue Wash?

The same difference applies the other way round: Atramentum Black is noticeably darker, much more muted.

ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.