Weapon Bronze vs Iridescent Copper Light (Coarse)

How close are they?

ΔE 19.8, loose: different enough that you should pick on purpose. Iridescent Copper Light (Coarse) is noticeably lighter, much more muted than Weapon Bronze. They are different kinds of paint: Army Painter Weapon Bronze is a metallic and Golden Iridescent Copper Light (Coarse) is a pearl paint, so they won’t behave the same on the model even where the colour is close.

Can I use Iridescent Copper Light (Coarse) instead of Weapon Bronze?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Iridescent Copper Light (Coarse) is noticeably lighter, much more muted than Weapon Bronze. They are different kinds of paint.

Can I use Weapon Bronze instead of Iridescent Copper Light (Coarse)?

The same difference applies the other way round: Weapon Bronze is noticeably darker, 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.