I thought this at first as well, I sent it to me busy who is an insulator enthusiast. I guess he's a bottle enthusiast too. He said is a "kick-up base" bottle
Yep... kick up base to an old wine or champagne bottle. Definitely NOT an insulator. Your next pic is the upper "hand tooled top" part of a prescription pharmacy bottle, ca 1900. Last pick is a fragment of a Chamberlain's Colic, Cholera and Diarrhoea Remedy patent medicine bottle. From Des Moines Iowa if I remember correctly.
What MD said was my first thought as well, but then I had to think about it and aren't the insulators solid except for the indentation? Never knew that those types of bottles were called kick-up... anyone know the origin/why this is what they are called?