Tourmaline Alchemy vs Rusty Metal

How close are they?

ΔE 16.1, loose: different enough that you should pick on purpose. Rusty Metal is a little lighter, more muted, warmer than Tourmaline Alchemy.

Can I use Rusty Metal instead of Tourmaline Alchemy?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Rusty Metal is a little lighter, more muted, warmer than Tourmaline Alchemy.

Can I use Tourmaline Alchemy instead of Rusty Metal?

The same difference applies the other way round: Tourmaline Alchemy is a little darker, more saturated, 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.