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The statement about machine-made bottles may seem contradictory (finer but more visually distinct) but is a function of the higher machine blowing pressure.Earlier machine-made bottles (1905-1920s) tend to have somewhat thicker/higher mold seams than later machine-made bottles due to the increasing precision in mold machining and machinery in general as time progressed.This mark is distinctive to the suction process which feeds glass into the bottom of an Owens machine's parison mold.
General Machine-made Diagnostic Features: Machine-made bottles will exhibit most or all of the diagnostic characteristics explained and illustrated below.
(This summary is largely an amalgam of Toulouse 1969b; Miller & Sullivan 1981; Jones & Sullivan 1989; Boow 1991; Cable 1999; Miller & Mc Nichol 2002; Miller & Morin 2004; empirical observations.) It should be noted that features #1, #3, #4, #5, and #6 are primary indicators of machine-made manufacture.
The machine is operated much as all pressing machines are..." (National Glass Budget 1910; Lockhart pers. This little bottle has a moderately narrow neck and a distinct valve or ejection mark on the base indicating press-and-blow machine manufacture. The 1908 photo below is from the Lewis Hine collection (Library of Congress) and shows an early, probably O'Neill (Barrett 2011) semi-automatic press-and-blow 4 mold milk bottle (which have relatively wide mouths) machine which came with the following caption: "Machine that blows 4 milk bottles at a time. Blowing air would have been supplied by the hose visible at the top of the set of blow molds to the left, where the final "blow" part of the cycle took place.
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).
"Ghost" seams are usually present on the neck, shoulder, and/or body of the bottle if made by a blow-and-blow machine (like the Owens Automatic Bottle Machine).
These are faint, somewhat wandering, hairline seams which if present (usually) are sporadically visible on the sides of machine-made 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.
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.
Be aware that bottles and jars made by early to mid-20th century press-and-blow machines do not usually have ghost seams, since the parison mold was usually one-piece, but will typically have a valve mark on the base (see #6 below). A suction scar is present on the base of Owens Automatic Bottle Machine produced bottles.