I just found a site, that details some of the behind the scenes information on the Props used on Doctor Who…

For example:

Original Cyberman costume pieces especially the fibreglass areas are one of the most difficult of all Doctor Who items to authenticate as so many have been replicated over the years that it is almost impossible to tell the difference this is worse on “earthshock”and “attack of the Cybermen” pieces but what makes items from “Silver Nemesis” different is the way in which they were finished, for the 25th anniversery story all the fibreglass parts were chrome plated and then lacquered but during filming the lacquer reacted with the chrome and started to turn gold!!

More information and tidbits, here Doctor Who Props