Prior to the outbreak of War with the British in 1812 there were but a scant few American Glass Factories engaged in the production of molded glass tableware. Instead, the wheel-cut and engraved wares that were the fashion of the day were supplied primarily through importation and trade with the English and Irish. However, in response to the onset of the War and the resulting cessation of foreign trade, an increasing number of American Glass Factories were built and/or modified to supply the domestic market with the cut and engraved glass to which the colonists were accustomed. The cut and engraved wares produced by these factories were nearly identical to the Irish and English imports in hopes not only of satisfying the utilitarian and aesthetic demands of the domestic market but also as a means of disproving the widely-held notion that "English glass is the best glass." And, though the American factories were in short time able to supply the market with a product "equal in quality to that of the imported wares," the signing of the Treaty of Ghent in 1815 and the resulting flood of inexpensive imported glass left the burgeoning American Flint Glass Industry in a quandary, as they could not compete with the cheap, but high-quality imports.
It is in the wake of the War and the resumption of trade then, that the glass we now refer to as "blown-three-mold" was first produced. The inspiration for blown-three-mold can be found in the cut and engraved imported glass with which it would soon compete and it is not unreasonable to say that blown-three-mold was born as an inexpensive alternative to English and Irish imports. Through the use of full-size three-piece-molds, American manufactures were able to simulate the deep cuttings and geometric patterns that made imported glass so popular. This process was MUCH more expedient than previous methods of cutting and engraving and as a result, American Glass factories were able to supply all classes of Americans with a commercial line of tableware at reasonable prices. Blown-three-mold glass then, can accurately be described as "the first distinctly American contribution to the evolution of molded glass tableware."
The distinguishing physical characteristic of blown-three-mold glass is the concavo-convex relationship between the inner and outer surfaces of the glass. Simply stated, the molded designs on the outer surface of a blown three-mold piece will be reflected by a corresponding hollow on the inner surface of the glass. This relationship is altered only when a piece is molded for design and significantly manipulated in its form (as in the case of dishes and bowls) or in the 1 in 100 objects that were blown using a particularly heavy gather of metal. As noted by the McKearins, it is this concavo-convex relationship that in conjunction with the particular qualities of blown molded glass that gives blown-three-mold the "liquid brilliance" to which the pioneer collectors so often referred.
It is also the McKearins who created the blown-three-mold "charts," which like their flask charts, remains the standard verbiage for modern collectors of blown-three-mold glass. The McKearin charts are separated into five distinct "groups," each with a number of different patterns that fall under the general heading of that group. Of the five groups, Group One (GI), Group Two (GII) and Group Three (GIII) are broadly referred to as "geometric," Group Four (GIV) as "arch" and Group Five (GV) as "Baroque." These five groups include more than 145 distinctly different patterns and innumerable minor mold variations. A dizzying number of different tableware forms were blown using these various molds, including bottles & flasks, decanters, castor bottles, toilet water bottles, drinking vessels, inkwells, hats, pitchers, celery vases, dishes & bowls, sugar bowls and salts.
producing these wares included (but were not imited to) the Kent,
Ohio Glass Works, the Mantua, Ohio Glass House, the Mount Vernon
Glass Factory, the Keene Marlboro Street Factory, the Coventry,
Connecticut Glass Factory, the Boston and Sandwich Glass Works
and the New England Glass Company. Of the 145 known patterns only
40 or so can be attributed with relative certainty to a specific
glass house. Blown-three-mold tablewares were produced using both
flint glass and ordinary "bottle glass" and though the
majority of BTM articles are clear in color, they can also be
found in earthy shades of green, brilliant yellows, fabulous blues
and beautiful shades of aquamarine. Of particular interest to
the modern collector are those wares blown of New England bottle
glass or flint glass wares in brilliant colors, although clear
items in unusual forms are also quite desirable.