1-color printing; desaturate or duotone?

[jimbrady]

If my printer does business cards full color front (4/1) and one color back (1/1) will a monochrome image work (on the 1/1)? Does it have to be duotone? I'm fuzzy on the difference as regards printing w/one ink color.

No, I can't call him on this--just answer me g)