We often receive email from folks who have discovered old bottles they think are old and valuable. It is never fun to reply and say that, although old, such bottles are extremely common and have little or no collector value. They’re simply not aware that many old bottles were mass-produced and remain today in large quantities.
Mass production of glass and bottles took off around 1910 or so, and it is not uncommon to find early 20th century wares in large quantities. Such bottles are mostly of clear or amber glass, with screw tops and mold seams that run to the top of the lip. Numbers, letters and other markings are found on their bases. Classic examples include Clorox bottles, Pitchers Castoria, Listerine, Vaseline, and Watkins medicines. Sadly, the success of such companies led to the manufacture of huge quantities of bottles and thus their lack of value today.
If you have located a trash dump with such glass, do not abandon all hopes of finding items of value. Milk bottles (mostly clear), poison bottles (mostly cobalt blue) and canning jars are good examples of more recently made glass objects that are not only collected but can be quite valuable. Also, trash dumps of the 20th century often contain discarded items of early years.