ΔE 81.0, poor: a clearly different colour, so not a substitute. Satin Varnish is noticeably lighter than Primer Black.
Not as a straight swap; see the closer alternatives below. Poor match (ΔE 81). Satin Varnish is noticeably lighter than Primer Black.
The same difference applies the other way round: Primer Black is noticeably darker.
ΔE is the colour difference between our two swatch estimates: under 2 is a perfect match (you’d struggle to tell them apart), under 6 very close, under 10 close, under 15 fair, under 20 loose, under 30 very loose, and 30 or more a poor match. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Primer Black on the colour wheel See Satin Varnish on the colour wheel
All matches: Primer Black equivalents · Satin Varnish equivalents