Westmoreland green satin center handled serving tray

A $2 thrift shop find today. It is 10" in diameter and about 4.5" high. I find many of these on ebay in many colors and styles, but with the same handle, most with no maker identified and age ranging from depression era to 1950s, though a couple claim the maker is either Tiffin or McKee. It was still a bit wet from washing and a couple of things that look like imperfections are from water streaking. It is mint. I wonder how they made this glass so impervious to thrift shop TLC? Satin have never been my favorite glass finish, but it is growing on my with these recent green pieces.