Dating milk glass
Perfumes and whisky and other alcoholic beverage bottles of this period often retained their cork closures.
The middle picture shows an open pontil on the base of a cylindrical medicine bottle.
The pictures below are from two early machine made medicine bottles.
I have put up pictures of the lips so that the readers can see how they mold goes all the way over the top as shown below. This is different than an older hand tooled, hand blown bottle.
In the 1920s, the bottle mimicked early forms which were hand tooled and sealed with a cork.
The automatic bottle machine was much more precise in gathering an exact amount of glass and the same amount of glass for each bottle this consistency lead to more uniform products.With the uniformity, came the possibility to create a solid seal with a screw cap.