ΔE 3.9, very close: most people won’t see a difference side by side. Ink Black is a little darker than Abaddon Black. They are different kinds of paint: Citadel Abaddon Black is an opaque base/layer paint and Vallejo Ink Black is an ink, glaze or transparent paint, so they won’t behave the same on the model even where the colour is close.
Yes, for most jobs. Very close match (ΔE 4). Ink Black is a little darker than Abaddon Black. They are different kinds of paint.
The same difference applies the other way round: Abaddon Black is a little lighter.
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.
See Abaddon Black on the colour wheel See Ink Black on the colour wheel
All matches: Abaddon Black equivalents · Ink Black equivalents