Quick Silver vs Obsidian Black

How close are they?

ΔE 16.1, loose: different enough that you should pick on purpose. Obsidian Black is noticeably darker, more muted than Quick Silver.

Can I use Obsidian Black instead of Quick Silver?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Obsidian Black is noticeably darker, more muted than Quick Silver.

Can I use Quick Silver instead of Obsidian Black?

The same difference applies the other way round: Quick Silver is noticeably lighter, 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.