Rusty Brass vs Ancient Copper

How close are they?

ΔE 24.2, loose: different enough that you should pick on purpose. Ancient Copper is noticeably lighter, more saturated than Rusty Brass.

Can I use Ancient Copper instead of Rusty Brass?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Ancient Copper is noticeably lighter, more saturated than Rusty Brass.

Can I use Rusty Brass instead of Ancient Copper?

The same difference applies the other way round: Rusty Brass is noticeably darker, 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.