With regard to recent discussion on ICON:
I have twice experienced the disappointment of purchasing what I thought was a very smooth, shiny insulator only to learn that it has this clear coating to obfuscate the fact that the surface is actually quite dull. The first was a CD 145 H.G.Co. yellow amber beehive that I won in one of the more popular insulator auctions that advertises on ICON. I paid north of $750 for it . . . or my wife did, since it was a Christmas present a couple of years ago. 8^) When I discovered the alteration (it came off in tiny flakes when I scratched it with my fingernail), I notified the auctioneer who contacted the consignor, and an agreement was reached to refund the amount I paid in excess of the opening bid, which was a substantial refund, and I believe I got a fair deal. I am convinced that neither of them knew about the coating. I never did get a photo of it with the coating still on, though. The rest of it came off with a short soak in an acid bath.
The second time I encountered this unpleasant surprise was on a fairly common CD 102 Brookfield SKEB with SDP in dark olive green. It was part of a package deal I got from another collector with whom I have done much business before and since. Since I didn't have much into it, I simply let him know about the coating and warned him to keep an eye out for it. He then checked with the person who sold it to him, and neither of them had any idea about the coating. I have no reason to doubt either of their veracity. I did get a photo of this one before I cleaned it.