A key way to date old soda bottles is by examining their mold seams, as the height and thickness of these seams often indicate the bottle's manufacturing technology and age.
Understanding Mold Seams for Dating
Mold seams are lines visible on glass bottles where the two or more halves of the manufacturing mold came together. As bottle-making technology advanced, the appearance of these seams changed significantly.
Here's how mold seams can help determine a bottle's age:
- Early Machine Production (circa 1905 - 1920s): According to one method, the mold seam height indicates how old the bottle is. Machine-produced bottles from 1905 through the 1920s typically exhibit mold seams that are higher and thicker. These pronounced seams are characteristic of the earlier machine blowing processes.
- Later Machine Production: As bottle manufacturing technology progressed beyond the 1920s, machinery became more refined. This led to the mold seams growing thinner.
- Modern Bottles: Eventually, the seams became incredibly thin, sometimes described as having the thickness of a hair.
By tracing the mold seam from the base of the bottle up towards the lip, you can get clues about the era it was produced. A seam that stops before the very top might indicate an earlier machine or even hand-finished lip, while a seam reaching all the way to the lip suggests later machine production.
While mold seams are a crucial indicator, dating old soda bottles often involves examining other features as well, such as:
- Bottle shape and style
- Color of the glass
- Maker's marks or logos on the base or side
- Style of the bottle's lip or finish
Combining the information from the mold seams with these other characteristics provides a more accurate estimation of the bottle's age.
