(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.
This potential for datable features is very useful since bottles are more often than not lacking embossing - an attribute which can often enhance dating opportunities.
The third picture shows the base of a milk bottle from just after the trun of the century.
The disk-like mark is sometimes confused with a pontil.
Unlike other books on the subject, that provide a diagram and step by step instructions Capt.To a lesser degree, the base can sometimes provide other information about a bottle like its intended function.This page provides some examples of how to use the website (primarily the Bottle Dating pages) to determine the approximate date or date range for various types of bottles made between the early 1800s and the mid-20th century.Because the bottom is hotter, it is also more fluid and has a tendency to sag, forming a shape like a spinning top which makes it unstable on flat surfaces.Giving a bottle an arched shape at the bottom means that if it does sag, it can do so without touching the bottom.