ΔE 10.9, fair: the same colour family, but not a straight swap. Obsidian Black is more muted than Burnt Iron.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Obsidian Black is more muted than Burnt Iron.
The same difference applies the other way round: Burnt Iron is 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.
See Burnt Iron on the colour wheel See Obsidian Black on the colour wheel
All matches: Burnt Iron equivalents · Obsidian Black equivalents