Copper vs Fulgurite Copper

How close are they?

ΔE 29.2, loose: different enough that you should pick on purpose. Fulgurite Copper is noticeably darker, more saturated, warmer than Copper.

Can I use Fulgurite Copper instead of Copper?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 29). Fulgurite Copper is noticeably darker, more saturated, warmer than Copper.

Can I use Copper instead of Fulgurite Copper?

The same difference applies the other way round: Copper is noticeably lighter, more muted, 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.