Mummified Grime vs Basilicanum Grey

How close are they?

ΔE 16.4, loose: different enough that you should pick on purpose. Basilicanum Grey is a little lighter, much more muted than Mummified Grime.

Can I use Basilicanum Grey instead of Mummified Grime?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Basilicanum Grey is a little lighter, much more muted than Mummified Grime.

Can I use Mummified Grime instead of Basilicanum Grey?

The same difference applies the other way round: Mummified Grime is a little 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.