Metal Grading . . . 

Clean Metal:  Metal stripped of all other types of metal, steel screws, fiberglass, insulation, And any other contaminating materials.

Dirty Metal:  Metals that are contaminated by other materials such as steel, other metals
insulation, fiberglass and other materials.

Mixed: Two or more non ferrous or ferrous metals together.  One metals always contaminates the other. If not cleaned and separated your metal will be bought as either mixed or dirty at a lesser price.

Separated:  All metals should be separate from one another in order to recycle them at their highest value.

Ferrous: Steel, iron magnetic metals

Non Ferrous: All other non magnetic metals