Boiler Black vs Bronze

How close are they?

ΔE 19.3, loose: different enough that you should pick on purpose. Bronze is noticeably darker, much more saturated than Boiler Black.

Can I use Bronze instead of Boiler Black?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Bronze is noticeably darker, much more saturated than Boiler Black.

Can I use Boiler Black instead of Bronze?

The same difference applies the other way round: Boiler Black 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.