The bases of dating
When referring to "markings" or "features" on the base of a bottle on this website, we are referring to embossing, mold lines, attached glass and/or mineral deposits which are confined within or around the edge of the bottle base.
(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.
The best readily available source for classifying bottle base shapes/profiles is the "Bottle Base Profiles" illustration that was previously included in the IMACS (Intermountain Antiquities Computer System) guide.
That guide is no longer available online through its long time host (University of Utah) although a copy of the entire bottle section is now (2015) available via this website at the following URL: Guide1992The base illustration by itself is available at the following link: illustration was taken from Richard Fikes' excellent 1987 book (now again in print) on historic medicine bottles - The Bottle Book: A Guide to Historic Medicine Bottles.
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.
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.
The bottom of a bottle is usually the thickest part, retaining more temperature throughout the production line.
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.