Dating antique drinking glasses
The offset is a function of the orientation of the parison relative to the two molds (parison and blow molds) used on the particular machine, or occasionally, to the hot parison "sticking" to the neck ring of the parison/blank mold when transferring to the blow mold (Ceramic Industry 19-15).
There are also no horizontal tooling marks present on the finish and/or upper neck as would be observable on the finish of mouth-blown bottles.2.
This mark is distinctive to the suction process which feeds glass into the bottom of an Owens machine's parison mold.
the suction scar on the base (point #5 above and picture to the left) can date no earlier than 1905 and are usually post-1910.
Though patented and first used to a limited degree in 1903, the first Owens Automatic Bottle Machine licenses were granted to other manufacturers in late 1904 making 1905 the effective "beginning" (i.e., terminus post quem) date for bottles with all of the above listed machine made diagnostic characteristics (Miller & Mc Nichol 2002).
These are faint, somewhat wandering, hairline seams which if present (usually) are sporadically visible on the sides of machine-made bottles.
The ghost seams are caused by the parison mold parts and if visible enough will be "attached" to the vertical seams in the finish.
Antique and vintage glassware encompasses countless types of decorative-yet-functional containers, bowls, and platters produced from the late 1800s through the mid-1900s.