Dating base 1
In short, there was (and is) nothing to stop a glassmaker from using an obsolete method in the production of a bottle.3.Some technological changes were expensive and not adopted by glass makers until it became an "adapt or perish" issue and many glass factories just perished.Utilitarian items makes up the bulk of the bottles produced during the 19th century and first half of the 20th century. Bottles intended to be used once to dispense the contained product without much hope of return, though as noted in #4 above, many types of bottles were commonly reused during the 19th and early 20th centuries; or 2.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.An example of this is the finding of a few pontil scarred utilitarian bottles among otherwise late 19th or early 20th century refuse.It is unlikely that this bottle was made during the same era, but instead was reused for a lengthy period or otherwise retained until broken or discarded.
Some bottle shapes are indicative of a particular manufacturing era, though many bottle styles/shapes were used for so many years - like the cylinder whiskey "fifth" or square snuff bottle - that the shape itself is not indicative of age.
Of course, soda & beer were reused up until quite recently.
The bottle pictured to the right has a Wait's Liver and Kidney Bitters label pasted over the embossing of a Star Kidney and Liver Bitters bottle!
Please be aware that in order to gain the maximum information about any particular bottle (e.g., dating, typing) the user must usually must review a number of pages within this website.
Unfortunately, the complexities of precisely dating bottles is beyond the scope of any simple key.