Pig Iron vs Old Gold

How close are they?

ΔE 28.8, loose: different enough that you should pick on purpose. Old Gold is noticeably darker, much more saturated than Pig Iron.

Can I use Old Gold instead of Pig Iron?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 29). Old Gold is noticeably darker, much more saturated than Pig Iron.

Can I use Pig Iron instead of Old Gold?

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

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.