Dark Elder Bronze vs Obsidian Black

How close are they?

ΔE 22.5, loose: different enough that you should pick on purpose. Obsidian Black is noticeably lighter, much more muted than Dark Elder Bronze.

Can I use Obsidian Black instead of Dark Elder Bronze?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Obsidian Black is noticeably lighter, much more muted than Dark Elder Bronze.

Can I use Dark Elder Bronze instead of Obsidian Black?

The same difference applies the other way round: Dark Elder Bronze is noticeably darker, much 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.