Some of this will be my opinion and is based on the piece that I have in hand and can compare with others. Some is based on the books I have ready at hand.
First we can totally dispell any connection with Durand Kimble. I have the book Durand The Man and His Glass by Edward Meschi. When one views the pictures of Durand glass, one is immediately aware of glass artistry at its best. The PK pieces or DK if you prefer don't even come close.
The word custard glass has been used and there again, in no way do these pieces stand up to the test of custard. Custard glass comes in various shades of yellow, usually very soft and will glow under a blacklight. My piece has no reaction to a blacklight.
Fireglo is the next term banded about. Fireglo has been attributed to the Boston and Sandwich glass company which closed in 1888. Since Durand did not start till 1897 we can safely assume no connection there.
Here is a piece of fireglo to show what it looked like.
http://glassgallery.yobunny.org.uk/displayimage.php?pos=-1585Rather nondescript and I would say somewhat grey in color. However backlit it takes on a whole new persona.
http://glassgallery.yobunny.org.uk/displayimage.php?pos=-1584My PK piece does not exhibit any sort of fire whatsoever. So in conclusion we can say definately what it is not. It is not Durand or Kimble, it is not custard, it is not fireglo. By eliminating what it is not, maybe we can move forward to what it is. Terry