ΔE 12.7, fair: the same colour family, but not a straight swap. Old Copper is a little darker, warmer than Balthasar Gold.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Old Copper is a little darker, warmer than Balthasar Gold.
The same difference applies the other way round: Balthasar Gold is a little lighter, cooler.
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 Balthasar Gold on the colour wheel See Old Copper on the colour wheel
All matches: Balthasar Gold equivalents · Old Copper equivalents