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.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.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).There are at least two additional finish related mold seams - one at the top of the finish which encircles either the bore or sometimes the outside of the upper lip portion of the finish (sometimes of these seams are present) and a horizontal seam immediately below the finish which circles the extreme upper neck (called a "neck ring parting line").
These are faint, somewhat wandering, hairline seams which if present (usually) are sporadically visible on the sides of machine-made bottles.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).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.The side mold seams on most machine-made bottles tend to be finer (narrower and lower) - though sometimes sharper and/or visually distinct than mouth-blown bottle mold seams although many mouth-blown bottles have very thick and distinct seams due to less precise mold construction or fitting.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.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).In any event, the suction scar is found on mouth-blown bottles though suction scars are sometimes referred to as a pontil scar by the unfamiliar.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.