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: There are a few machine-made bottle types (milk, shoe polish and small ink bottles) or post-production processes (fire polishing) which exhibit mold seams in the finish/upper neck that deviate from the descriptions in points #1 and/or #3 above; these bottles may appear to be of mouth-blown manufacture.
These deviations are discussed on the main Bottle Dating page in a box under 4.
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.
(Note: A movie clip showing this process in action is linked at the bottom of this box.) Suction scars can not be produced by feed and flow automatic machines (i.e.
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).
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: 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.