Dating 20th century
Pontiled base fragments could also be from later produced "specialty" bottles which are described below.5.
Heavy duty bottles intended to be recycled and reused by the producer or distributor of the contained product (primarily soda, beer & milk bottles); or 3.
A substantial amount of bottle type specific information must be reviewed by a user to increase the probability of dating accuracy.
Additional reference materials outside of this website must often be consulted to narrow down the date of any item as far as is possible and to really get a "feel" for the history of the bottle in question.
Utilitarian items include canning/fruit jars and figured flasks since they were intended to be reused by the purchaser and have been observed to follow well the dating guidelines, though there are some manufacturing timeframe differences with canning jars.
(Click canning jar to view the typology page section devoted to that category.) The beer bottle pictured to the above left is a classic example of a utilitarian bottle from the late 19th century that was typically reused.