Ancient Sepia vs Black Wash

How close are they?

ΔE 46.7, loose: different enough that you should pick on purpose. Black Wash is noticeably darker, much more muted than Ancient Sepia.

Can I use Black Wash instead of Ancient Sepia?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 47). Black Wash is noticeably darker, much more muted than Ancient Sepia.

Can I use Ancient Sepia instead of Black Wash?

The same difference applies the other way round: Ancient Sepia is noticeably lighter, much more saturated.

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.