Old Copper vs Copper

How close are they?

ΔE 21.6, loose: different enough that you should pick on purpose. Copper is a little darker, cooler than Old Copper.

Can I use Copper instead of Old Copper?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Copper is a little darker, cooler than Old Copper.

Can I use Old Copper instead of Copper?

The same difference applies the other way round: Old Copper is a little lighter, warmer.

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.