From the factory some of them have a coating that develops with age that comes off with elbow grease. You can see in his last pic where he removed it to show the part number in the rubber. That pair is on the dirty/old side of the realm, but the rubber is not affected.

Pads are the same thing from 72-93. Pretty sure they went NS1 about 2 years ago, about early 2012. They were all over ebay then evaporated.