Steampunk Copper vs Forged Red

How close are they?

ΔE 24.0, loose: different enough that you should pick on purpose. Forged Red is noticeably darker, much more saturated, cooler than Steampunk Copper.

Can I use Forged Red instead of Steampunk Copper?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Forged Red is noticeably darker, much more saturated, cooler than Steampunk Copper.

Can I use Steampunk Copper instead of Forged Red?

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