This article is from the RCA SelectaVision VideoDisc FAQ, by firstname.lastname@example.org (Tom Howe) with numerous contributions by others.
The coating applied to CED's was intended to reduce stylus wear, but its
presence is not necessary for the disc to play. Actually, RCA found that
this coating doubled the life of the stylus tip, and only to a lesser
degree increased the life of the disc. And the coating is a silicone
compound, so it is not evaporative, and probably has better long-term
stability than the organic PVC of which the disc itself is made.