Are you talking about the die cast window crank handles? If so, see page 12-7 of the "Restoration Guidelines" and tell me which style handle you have and what year and body style vehicle.
Style D should be bright nickel. Styles M & U can be either bright nickel or Butler nickel, depending on what year and body style it is in.
Reproduction Style D handles are easy to distinguish because of the knob with the bump in the center. Original style D handle knobs are smooth.
Every reproduction handle that I have ever seen was chrome plated.
Now, if you are talking about the "window crank mechanisms", that is a different can of worms.
Don Turley
www.donturley.com