Any thoughts on the maker of this mid century light fixture?  

I would love to find out who made this fixture, and when.  The only sticker I can find is the "union made" one.  The number on that, if it helps anyone, is "C 21867321"It seems to be a very high quality piece in terms of it's construction and materials.  I have seen a few very distinctive similarities to some Lightolier fixtures, but I have nothing else to go on.  My last request in this forum for an ID of a lamp was answered with an image from an old catalog.  I'm hopeful someone might have a similar reference for this piece.Any help would be greatly appreciated.