Dating industry trends
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."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."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).
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.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.: 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.