Ancient Sepia vs Umber Wash

How close are they?

ΔE 34.7, loose: different enough that you should pick on purpose. Umber Wash is noticeably darker, much more muted, warmer than Ancient Sepia.

Can I use Umber Wash instead of Ancient Sepia?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 35). Umber Wash is noticeably darker, much more muted, warmer than Ancient Sepia.

Can I use Ancient Sepia instead of Umber Wash?

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

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.