Usualy, they are stainless steel. ALL those I saw where that way.
If that's your case, use some abrasive powder or soap, maybe with some fine steel wool.
Now, it's just a mather of vigorous scrubbing and elbow grease.
If there are lime deposits, using some vinegar or other mild acid will greatly help dissolvint it.
If you use some stronger acid, be sure to use thick rubber gloves.
Electro, February 2014