John Bartley has it pretty well covered. I would like to add one other thing. We ALWAYS carried a can or two of WD40. When you take the blade off the mill, it "Should" be relatively clean, or, at least, wet-damp.
Spray a little WD on both sides of the blade and use a rag dampened with WD, to wipe the blade down. We always carried the original shipping boxes (Cardboard), and coiled the blades and put them in the box(es).
Then, when you are ready to sharpen, the blades are clean and rust free.