Burnt Iron vs Obsidian Black

How close are they?

ΔE 6.5, close: similar, with a visible difference side by side. Obsidian Black is more muted than Burnt Iron.

Can I use Obsidian Black instead of Burnt Iron?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Obsidian Black is more muted than Burnt Iron.

Can I use Burnt Iron instead of Obsidian Black?

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.