One of the things that really confused me when I first became interested in early colonial period black glass, was how to easily tell English produced pieces from Dutch or Belgian bottles. Depending on where they spent the past 2 or 3 hundred years, and considering the wide variations in (lip) finishes, surface wear, and patina gathered over the decades and centuries, I saw many "light" English pieces offered as Dutch, and many "dark" Dutch pieces offered as English. The two primary distinguishing features you really have to watch for are the thickness (and weight) of the glass used in production, and the type of pontil scar within the basal cavity or "kick-up". With some exceptions, early English black glass was thicker and/or heavier than what was normally used in the manufacture of "Dutch" bottles of very similar design. By "Dutch", I mean bottle types produced in Holland (Netherlands) and Belgium for the most part, taking the so-called "onion" types as an example. The English version of the "onion" was normally much darker, at least in "apparent" coloration, because of the heavier and/or thicker glass used in their production, as well as the higher iron oxide content used in the making of the actual glass. Much English black glass also tends to have more of an amber tint, whether amber-tinted olive green or nearly solid amber tone in color because of the extra oxides used. Many of the "Dutch" onions also tend to have somewhat longer, and often times wider necks than their English counterparts which had more of a pushed down or "squat" body compared to the more "bulbous" Dutch onions. Obviously, with mouth-blown bottles, there is sure to be a wide variation in both types. But the one thing to look at first in distinguishing "English" from "Dutch" is the pontil. Again, with some exceptions, the early English black glass bottles will bear a large sand pontil scar on their base as opposed to the smaller diameter "open" or blowpipe pontil scar normally seen on Dutch and Belgian bottles. Also, there are sometimes subtle differences in the lip and string "finishes" between the two types, though there was so much overlap and variation in the earlier (pre-1740) bottle styles that it is often hard to make any determination of provenance based on that characteristic alone. That was not the case with later cylinder types as was shown by the excellent work of Olive R. Jones in "Cylindrical English Wine and Beer Bottles: 1735-1850". As with any of this information on primarily pre-1840 English black glass, what you end up with is a "general rule of thumb", but no absolutes.
Another misnomer I often see in describing later (~1740 to 1820) cylinder style black glass bottles, is the use of the term "free blown", when in fact, dip molds were being used by about the time that the cylinder style bottles came of age. Some think this may have been the case just near the end of the onion bottle types, although there are "transitional mallets" dating between the onion and mallet that were obviously "free-blown" without the use of the dip mold just prior to its use in production of the true straight-sided mallets. But here again, there are known examples of true mallet shapes, both free-blown and others blown with the use of dip molds. There was much use of true "molds" in the blowing of bottle glass at least as far back as first century A.D. Rome, contrary to the common misconception that true "blown-in-mold" bottles didn't come along until the 1820s or so. In some respects, even the earlier "core-formed" bottles made in the centuries B.C. were basically a type of "reverse" molding process. But dip mold bottles are too often passed off or overlooked as truly "molded" bottles, in favor of those later pieces produced with the advent of the two and three-piece molds of the early 19th century.
One thing that I have learned over the years is that one person can look at a shelf of black glass bottles and see "nothing but a bunch of old, ugly, black bottles covered in dirt", but after some interest and study, see a wonderful example of glass bottle evolution that spanned a period of approximately 1630 into the 1870s or 80s, some 250 years or so longer than what most of us see as "truly old bottles".
Yes, thank you for your educational and enlightening post! Early "Black Glass" is one area that I personally would like to learn more about, however, rarely get the opportunity to make such comparisons as you have made. It seems that there are only a handful of real students researching the characteristics of different origins... so it is always a pleasure to learn about such findings.
I have a couple of quick questions... How does the early American 18th century black glass fit into your findings? Understandably, such glasshouses as Germantown and Wistarburgh blew bottles in the methods that specific glassblowers learned from their homelands overseas, however, have you been able to identify specific characteristics which you can call American? Generally, most of the 18th century American glass that I have seen is in the German tradition such as the forms and techniques, however, similar pontil characteristics as the English black glass. Anyways, it would be nice to hear your thoughts on the early American glass.
I wanted to ask your opinion of this large handled pitcher. It looks late 18th or early 19th century, however, I am not sure of the origin. Do you have any thoughts on it?