These vertical seams - finish mold seams vis--vis the upper neck mold seams - may range from just slightly offset to 90 degrees offset (like shown at the linked image above).The offset is a function of the orientation of the parison relative to the two molds (parison and blow molds) used on the particular machine, or occasionally, to the hot parison "sticking" to the neck ring of the parison/blank mold when transferring to the blow mold (Ceramic Industry 19-15).This bottle dating "key" is a relatively simple "first cut" on the dating of a bottle.While running a bottle through the key questions, the user is frequently directed to move to other website pages to explain diagnostic features and concepts as well as to add depth and/or precision to the initial dating estimate.By the mid-19th century, embossed lettering and marking on bottle bodies and bases, denoting manufacturers and products, made more precise dating possible. Is the bottle highly symmetrical, but lacking mold seams?In addition to technology, products and manufacturers, certain types of glass colors will also aid in dating. This type of bottle was probably dip-molded and dates after circa 1820.There are also no horizontal tooling marks present on the finish and/or upper neck as would be observable on the finish of mouth-blown bottles.2.
(This summary is largely an amalgam of Toulouse 1969b; Miller & Sullivan 1981; Jones & Sullivan 1989; Boow 1991; Cable 1999; Miller & Mc Nichol 2002; Miller & Morin 2004; empirical observations.) It should be noted that features #1, #3, #4, #5, and #6 are primary indicators of machine-made manufacture.I have put up pictures of the lips so that the readers can see how they mold goes all the way over the top as shown below. This is different than an older hand tooled, hand blown bottle.The pressure from the automatic machine was strong and the molds fit tight leaving only a very thin line.Dating antique bottles requires knowledge of the evolution of bottle technology and the ability to research manufacturers and bottling companies.Although glass bottles have been made for a few thousand years, it was not until the 19th century that bottle use became common, coinciding with the industrial revolution. The earliest bottles were hand-blown by a glassblower with a blowpipe and lack seams.The information on this website will, however, usually produce a reliable manufacturing date range for a majority of American utilitarian bottles manufactured from the early 1800s to the mid-20th century.Using physical, manufacturing related diagnostic features, most utilitarian bottles can usually only be accurately placed within a date range of 10-15 years (i.e., 1870-1880 or 1885) . Like many industries making the leap from manual craftsman production to industrialization and automation, technological advances in bottle manufacturing were not immediately accepted by glass manufacturers or their workers.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.A pontil rod held the nearly molten bottle during the final stages of manufacture.The scar was left when the pontil was detached from the bottle. If the seams disappear in the neck, the bottle was probably "blown-in-mold" and dates circa 1820 to early 1900s.