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(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.
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.
Bottles which have all the primary characteristics noted above (#1, #3, #4) bottles.
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).
This is accomplished so that there is no perceptible mark upon the bottle showing the joint, and the bottle stands every possible test as to strength. Although products of this machine are not conclusively known a bottle such as the one at this link - offset seams shoe polish bottle - may well be a product of the described machine as there is a distinct and abrupt interface edge at the shoulder where the mold seams for both the body and neck end and are offset. This two table semi-automatic machine would have been hand fed with glass (furnace likely to the right) and does have the two different mold sets with the parison molds (where the first "press" part of the cycle took place) the set on the right.
The ghost seams are caused by the parison mold parts and if visible enough will be "attached" to the vertical seams in the finish.
Click on ghost seam to view a close-up explanatory picture of this attribute.