Fulgurite Copper vs Chestnut Gold

How close are they?

ΔE 22.0, loose: different enough that you should pick on purpose. Chestnut Gold is a little darker, much more muted than Fulgurite Copper.

Can I use Chestnut Gold instead of Fulgurite Copper?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Chestnut Gold is a little darker, much more muted than Fulgurite Copper.

Can I use Fulgurite Copper instead of Chestnut Gold?

The same difference applies the other way round: Fulgurite Copper is a little lighter, much more saturated.

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.