Mortarion Grime vs Brown Wash

How close are they?

ΔE 22.6, loose: different enough that you should pick on purpose. Brown Wash is noticeably darker, warmer than Mortarion Grime.

Can I use Brown Wash instead of Mortarion Grime?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Brown Wash is noticeably darker, warmer than Mortarion Grime.

Can I use Mortarion Grime instead of Brown Wash?

The same difference applies the other way round: Mortarion Grime is noticeably lighter, 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.