Broadsword Silver vs Iridescent Silver (Fine)

How close are they?

ΔE 19.8, loose: different enough that you should pick on purpose. Iridescent Silver (Fine) is noticeably lighter than Broadsword Silver. They are different kinds of paint: Army Painter Broadsword Silver is a metallic and Golden Iridescent Silver (Fine) is a pearl paint, so they won’t behave the same on the model even where the colour is close.

Can I use Iridescent Silver (Fine) instead of Broadsword Silver?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Iridescent Silver (Fine) is noticeably lighter than Broadsword Silver. They are different kinds of paint.

Can I use Broadsword Silver instead of Iridescent Silver (Fine)?

The same difference applies the other way round: Broadsword Silver is noticeably darker.

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.