This distinctive base scar is easier to illustrate than describe; click on suction scar for a picture of a typical scar which exhibits the diagnostic "feathering" that surely indicates Owens machine production (same image is below left).This mark is distinctive to the suction process which feeds glass into the bottom of an Owens machine's parison mold.On many early (very early 1900s into the 1920s) and occasional later (1930s and later) machine-made bottles the vertical body/neck and finish mold seams are discontinuous and offset from each other; click offset seams for a picture of this attribute.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).
Feature #2 (mold seam diameter) is not as strongly diagnostic as the primary indicators as mouth-blown bottles sometimes can have very fine mold seams.
Feature #7 describes a couple glass related features that are quite consistent in machine-made bottles, but not diagnostic, i.e., mouth-blown bottles may sometimes have few/no bubbles in the glass and even thickness.
(Note: the term "parison mold" and "blank mold" are synonymous for the first mold in the two mold machine process.): (see the Note box below point #3 for an exception) run up to the highest point of the finish and often onto the extreme top finish surface (i.e., onto the rim or lip).
See the machine-made section of the Bottle Bases page for more information on these scars. with distinct suction scars were likely Owens machine produced.)6. Machine-made bottles tend to have few if any bubbles in the glass and the thickness of the glass is usually more uniform throughout the bottle as compared to mouth-blown bottles.
(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.