Picked this specimen up from a dealer at the 2016 Springfield Show. This example (on the right side of the joined photo) shows almost all the classic signs of being heat altered:

1) the slumping of the insulator in comparison to a hoopskirt that is not slumped; 2) the roughness of the base surface (see right side photo). The glass should be smooth. 3) the flattening of the the base surface (see right side photo). The base should be rounded in profile. 4) the heat alteration appears to have caused an annealing fissure to crack wide open. This is another alteration characteristic that I have not observed before.