(Note: It is likely that other types of suction based automatic bottle machines made in Europe in the 1920s - and possibly later - also produced a suction scar on the base of their products [Pearson 1928]. The presence of a circular valve mark on the base of a bottle (typically a wide mouth bottle or jar) is sure evidence of machine-made manufacture by a press-and-blow machine. This is especially true of later machine made bottles, i.e. (Note: The presence or absence of bubbles in the glass and relatively even distribution of the glass throughout the characteristic is not a primary feature of either machine-made or mouth-blown bottles, though there are strong trends.
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.
Added evidence to this theory is that an identical shape and size (2 oz.) "Round Shoe Polish" bottle is shown in the "Machine Made Ware" section of Cumberland's 1911 catalog (Cumberland Glass 1911). Very few narrow neck bottles made on the Owens machines will pre-date that time also. 2007d].) It is thought that probably all pre-1905 semi-automatic bottle machine production in the U. was relegated to wide-mouth bottles/jars due to limitations of the press-and-blow machines at that time (Toulouse 1967; Miller & Sullivan 1981; Jones & Sullivan 1989; Cable 1999; Miller & Mc Nichol 2002; Lockhart pers. This image (click to enlarge) also shows that on many early press-and-blow machines the parison mold was one-piece (note absence of mold hinges) as the narrow non-inflated parison could be removed from either the base or finish mold end (depending on the type machine) whereas the blow mold had to be two-piece (hinges obvious) to remove the expanded and finished bottle if there was any narrowing from the body to the neck/finish (like a typical milk bottle would have).
"gob feeders") though a similar type mark without the feathering is induced by the parison/blank mold of most other blow-and-blow machines - including up to the present day.
Press-and-blow machines usually have a round valve mark on the base but lack either the suction or parison scars.
These vertical seams - finish mold seams vis--vis the upper neck mold seams - may range from just slightly offset to 90 degrees offset (like shown at the linked image above).
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).