Purple Tone vs Atramentum Black

How close are they?

ΔE 41.6, loose: different enough that you should pick on purpose. Atramentum Black is a little lighter, much more muted than Purple Tone.

Can I use Atramentum Black instead of Purple Tone?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 42). Atramentum Black is a little lighter, much more muted than Purple Tone.

Can I use Purple Tone instead of Atramentum Black?

The same difference applies the other way round: Purple Tone 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.