The bases in dating
Giving a bottle an arched shape at the bottom means that if it does sag, it can do so without touching the bottom.(British Glass 2004) In conjunction with the finish (lip), the various attributes and features found on the base of a bottle allows for some of the better opportunities for the manufacturing based dating of a bottle.For more information on the subject of glassmaker markings see the Makers Marks page, which is a sub-page linked to the Glassmaking & Glassmakers page.This page is divided into two sections based on the primary methods by which bottles were manufactured - mouth-blown (hand-made) or machine-made (both semi and fully automatic) - since base features on these types of bottles generally differ significantly.
(See the Bottle Morphology page for more information on the major parts of a bottle.) covered in any depth on this page is the base profile or shape.On machine-made bottles additional markings can be the product of the automated machinery which produce the bottle, but which are not part of the mold itself.Most significant here are markings related to the feeding of the glass to the mold - a subject covered later on this page in the "Machine-made bottles" section.: The bases of many bottles have embossing or symbols that pertain to the product that the bottle was designed to contain and/or the producer or bottler of the product.There is also large section on pontil marks or scars due to its size (hyperlink found several places below).Short differentiating informational statements are provided below (in bold) to make an easy "break" between mouth-blown and machine-made bottles.
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The bottom of a bottle is usually the thickest part, retaining more temperature throughout the production line.