One approach to helping beginner identify their old bottles involves show them the bases of old bottles.
The picture below at the left shows an iron pontil on the base jof a historical flask circa 1865.
The middle picture shows an open pontil on the base of a cylindrical medicine bottle.
The pressure from the automatic machine was strong and the molds fit tight leaving only a very thin line.
In the neck on the right notice how just below the collar the mold seam goes complete around the neck. Both of these medicine bottles look much like their earlier counterparts.
This was the manner in which the early Owens bottles were blown. the step out collar of the example on the left is characteristic of bottles of the late teens and 1920s.
the bottle on the right appears to have a tapered collar a form which was very popular for more than 60 prior to the making of this bottle.
This is the base of the bottle whose lip is shown above left.