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The disk-like mark is sometimes confused with a pontil.
the pontil is actually broken glass where the metal rod used to hold the bottle while the lip was form was broken off leaving a sharp scar.
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.
The base of the second bottle whose lip was shown above right is displayed here.
The the lower left corner you can see evidence of the diagonal mold seam which at one time bisected the base.
This is the base of the bottle whose lip is shown above left.
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.
Note the diagonal line which cuts across the base is obliterated by the Owens Ring (the large off-center curcular feature). the base is crudely made for a machine made bottle.
Owens' early bottles were often cruder than their hand blown hand tooled counterparts.the right side is crude and was disturbed by the action of marking the marking with Owens Ring.