Gemstone Red vs Old Copper

How close are they?

ΔE 30.0, loose: different enough that you should pick on purpose. Old Copper is a little lighter, much more muted, warmer than Gemstone Red.

Can I use Old Copper instead of Gemstone Red?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 30). Old Copper is a little lighter, much more muted, warmer than Gemstone Red.

Can I use Gemstone Red instead of Old Copper?

The same difference applies the other way round: Gemstone Red is a little darker, much more saturated, cooler.

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.