Pontil scars on dating glass
All of the bottle mouths shown below were machine made.In the 1920s, the bottle mimicked early forms which were hand tooled and sealed with a cork.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.
The pictures below are from two early machine made medicine bottles.the right side is crude and was disturbed by the action of marking the marking with Owens Ring.Owens rapidly made improvements as eh redesigned his machine numerous times and eventually over came the problems of uniformity see here.Lettering on the body will give clues to the contents and lettering on the base will give clues to the manufacturer.Both require more specific research to refine the bottle's date beyond observation of technology. Bottles with a purplish or amethyst hue are made from manganese dioxide glass and date circa 1880 to 1920.
Bottles with suction scars were made in an Owens Automatic Bottle Machine and date after 1903.