We bought a corner china cabinet from a consignment shop. I don't have any details about age, manufacturer, etc. It's a medium brown wood with glass shelves. At the upper shelf is a sort of shell-shaped piece of the same wood forming a curved top. It has one-inch wide ridges...I don't know exactly how to explain this, obviously...On the ridges there is a gray substance. It comes off easily with a finger rub. It's kind of attractive and I wonder if it's some kind of antiquing color...or just gray dust that accumulated over the years. Anyone have any ideas whether I should clean it or just leave it the way it is and enjoy it? Thanks.