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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.It was noted in 1910 that the Cumberland Glass Company (Bridgeton, NJ) had "...succeeded in perfecting a machine that will satisfactorily produce narrow neck bottles, such as catsups, beer bottles, etc., at a big saving over the hand method." The method used was unusual and may have been unique in bottle-making history: "The machine differs from all others, and in getting the neck upon the bottle, the vessel is made in two sections, the neck being put upon the bowl with a second operation. Manager says machines are fast coming into play in bottle industry, plans eventually to have machines in place of "carrying in boys." Location: Clarksburg, West Virginia" (Library of Congress).
In the glassmaking trade, these seams along with the side mold seams within the finish or just below are referred to as "neck ring" or "neckring" seams since they were formed by the separate neck ring portion of a machine mold (Tooley 1953).
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").
Click on the picture to the left to view an illustration which shows both of these seams or click machine-made finish to view an image which shows well the seam below the finish.
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.