Iron Hue vs Ancient Copper

How close are they?

ΔE 63.3, loose: different enough that you should pick on purpose. Ancient Copper is noticeably darker, much more saturated than Iron Hue.

Can I use Ancient Copper instead of Iron Hue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 63). Ancient Copper is noticeably darker, much more saturated than Iron Hue.

Can I use Iron Hue instead of Ancient Copper?

The same difference applies the other way round: Iron Hue is noticeably lighter, much 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.