Base of the Bottle Markings In most cases, one- or two-digit numbers are actually mold numbers that indicate the specific bottle mold or section in an automatic bottle machine. Base numbers also indicate bottle styles or shapes, manufacturing dates, or factory location codes.

What are the numbers on the bottom of old bottles?

Many bottles carry only a number (or numbers) on the base. These marks usually served as some type of mold identification, indicating a particular mold used by a glass factory. If a number of identical molds were produced for making a certain type of bottle, they would often be serially numbered (such as 1 to 12).