Rust Tone vs Sepia Wash

How close are they?

ΔE 34.3, loose: different enough that you should pick on purpose. Sepia Wash is noticeably lighter, much more muted than Rust Tone.

Can I use Sepia Wash instead of Rust Tone?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 34). Sepia Wash is noticeably lighter, much more muted than Rust Tone.

Can I use Rust Tone instead of Sepia Wash?

The same difference applies the other way round: Rust Tone is noticeably darker, 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.