The bases of both mouth-blown and machine-made bottles have various features and/or makings which can greatly assist in determining or narrowing down the age of the bottle.
To a lesser degree, the base can sometimes provide other information about a bottle like its intended function.
For additional information, click Dating Page to go to the pertinent section of that describes the differences between these bottles.
Once you have determined which type bottle you have - or if you know already - click on one of the following links to move directly to that section of this page (there are numerous links back to this index scattered throughout the page): A.
Markings or features on the base of a bottle are usually formed either by the mold or by a pontil rod (or punte)..both.
For example, overall the three bottles in the picture at the top of the page are (from left to right) - octagonal, rectangular, and square.
However, the rectangular and square bottles also have distinctly beveled edges and the octagonal bottle is actual round right at the heel of the bottle - all of which complicate describing the base profiles a bit.
These are usually some type of embossed letters, symbols, and/or numbers which were molded onto the base of the bottle for a variety of glassmaker determined reasons.
Click Owens-Illinois bottle base to view a picture of the relatively elaborate bottle base mold markings used by the Owens-Illinois Glass Company during the mid-20th century.