Moonstone Alchemy vs Aged Metal

How close are they?

ΔE 16.4, loose: different enough that you should pick on purpose. Aged Metal is more saturated, cooler than Moonstone Alchemy.

Can I use Aged Metal instead of Moonstone Alchemy?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Aged Metal is more saturated, cooler than Moonstone Alchemy.

Can I use Moonstone Alchemy instead of Aged Metal?

The same difference applies the other way round: Moonstone Alchemy is more muted, warmer.

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.