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.

How do I know if my old bottles are valuable?

While not all old bottles are valuable, an older bottle is more likely to be worth more than a newer one. Seams and pontil marks are two of the ways you can determine a bottles age. The pontil mark is the mark at the bottom of the bottle where it was attached to the glass blowers pontil rod.