Dating Antique Bottles by Mold Seams
Dating bottles can be a frustrating experience for the average garage saler, part time eBay seller or beginning collector. Bottles were so widely used for so many purposes—from rot gut whisky to feminine ointments—no one reference book can identify and date all the examples you might encounter.
One of the easiest ways to date bottles is to examine their mold seams. The mold seams are faint lines formed where two or more parts of the bottle mold met when the bottle was made. Most seams are quite obvious especially when the glass is held to the light. A magnifying glass may be helpful for particularly faint seams, but certainly not necessary.
Seams are a reliable guide to age due to changes in how bottles were made. When bottles were free blown into molds, the bottle was made first then a lip was added. Since the lips were made last, they have no mold seams. Bottle machines, by contrast, begin the bottle-making process with the lip which produces a mold seam running across the lip and down the entire length of the bottle. As a reliable general rule, the farther the seam comes up the side, the newer the bottle. (see comparisons in Figs. 1 and 2.)
Keep in mind that production dates are not absolute dates; different bottle factories changed their equipment and production methods gradually. The different methods of bottle production should be considered as eras, not a series of abrupt changes.
- Guidelines for Determining the Age of Antique Bottles
Historic Glasshouse: Additional information on dating glass bottles.
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Additional information for dating antique and vintage glass bottles: The Depot