Rough Iron vs Pig Iron

How close are they?

ΔE 24.4, loose: different enough that you should pick on purpose. Pig Iron is noticeably lighter, more muted than Rough Iron.

Can I use Pig Iron instead of Rough Iron?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Pig Iron is noticeably lighter, more muted than Rough Iron.

Can I use Rough Iron instead of Pig Iron?

The same difference applies the other way round: Rough Iron is noticeably darker, 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.