ΔE 13.3, fair: the same colour family, but not a straight swap. Archaic Sepia Wash is more saturated than Valhallan Blizzard. They are different kinds of paint: Citadel Valhallan Blizzard is a technical paint or medium and Two Thin Coats Archaic Sepia Wash is a wash/shade, so they won’t behave the same on the model even where the colour is close.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Archaic Sepia Wash is more saturated than Valhallan Blizzard. They are different kinds of paint.
The same difference applies the other way round: Valhallan Blizzard is more muted.
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 Valhallan Blizzard on the colour wheel See Archaic Sepia Wash on the colour wheel
All matches: Valhallan Blizzard equivalents · Archaic Sepia Wash equivalents