ΔE 17.0, loose: different enough that you should pick on purpose. Ancient Copper is noticeably lighter, more saturated than Fire Opal.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Ancient Copper is noticeably lighter, more saturated than Fire Opal.
The same difference applies the other way round: Fire Opal 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.
See Fire Opal on the colour wheel See Ancient Copper on the colour wheel
All matches: Fire Opal equivalents · Ancient Copper equivalents