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Mold-Blown and Pressed Glass
There seems to be considerable confusion regarding the mold-blown and pressed or pattern types of glass. Possibly this is because both types have two things in common. Both originated as inexpensive substitutes for the fine cut glass imported from England, Ireland, and the continent of Europe. Both were shaped in molds but with a drastic difference of method.
Mold-blown was the earlier type, being in vogue from about 1820 to 1840. Hollow molds made in two, three, or four vertical leaves hinged together were used. These were of iron and the interiors intaglio-cut in designs simulating those of cut glass. When the leaves of such a mold were assembled, the upper end was open and into it was inserted a blowpipe with a gather of hot molten glass. The glass was inflated by the glass blower and quickly took on the shape and design of the mold. Then the mold was opened and the piece still attached to the blowpipe removed. After that it was finished by the usual glass-blowing manipulations. This technique antedated the Christian Era and was extensively used by glass workers of the Roman Empire.
Pressed glass, on the contrary, was a product of the nineteenth century and was the first radical change in glass-making in over two thousand years. Its introduction resulted in a still cheaper imitation of costly cut glass. By this process the red-hot molten glass was pressed into the mold rather than blown. This was accomplished by a plunger affixed to a long lever-like handle which was pressed down on the charge of glass forcing it into the incised design cut in the mold. Then the piece was removed from the mold fully shaped.
While this is the major difference between the mold-blown and pressed glass, there are minor differences: the mold-blown is lighter and thinner; its design in reverse may be felt on the inside and generally there is some trace on the bottom of the piece of where the pontil or handling rod was attached. A piece of pressed glass is heavier and thicker; its inside surface is always smooth and naturally there is no pontil mark on the bottom.
Pressed glass went beyond the aims of the mold-blown in producing a cheap and attractive imitation of cut glass. It revolutionalized the glass industry and by the second half of the nineteenth century practically no home was without a good supply of this tableware in varied patterns.
Mold-blown glass, on the other hand, was made for only about thirty years. Originating in Ireland, its manufacture was widespread in the United States between 1820 and 1850. The technique was probably introduced here by Irish glass blowers who migrated to America during the early years of the century. This glass was produced in quantity by various glass houses in New England, the Pittsburgh area, and Ohio. Some of these factories were shortlived; others eventually turned to the cheaper and more quickly made pressed glass.
Mold-blown was produced mostly in geometric designs, with over five hundred patterns. The objects made include such tableware as plates, goblets, wine glasses, pitchers, celery vases, and decanters, the last being the most common of the pieces that have survived. Other articles were flasks, lamps, inkwells, vases, jars, food holders for bird cages, hats, witch balls, and some miniatures. These were in clear flint glass as well as various shades of green, blue, red, and purple.
Examples in Illustration 69 are all of clear glass and show the variety of objects made as well as the prevalent designs. The early pieces are usually geometric in design but baroque patterns appeared to some extent later. Decanters and water glasses were especially popular, the latter flaring, straight, or barrel-shape as shown in the top and middle rows. Decanters followed the shapes and sizes of the cut-glass ones; the stoppers might be sunburst, hollow knob, or plain like that of the vinegar cruet in the middle row second from the right. Wine glasses, whale oil lamp, hat inkwell, and small pitchers on the bottom row are typical of other pieces in favor at the time. The geometric motifs most commonly used have been given present-day names that are sufficiently descriptive: waffling, ribbing, sunburst, sunburst-in-square, and bull's eye sunburst. They appear, singly or in combination, in the pieces illustrated.
Mold-blown glass had a definite appeal during the few years of its manufacture, but it was so fragile that examples are now rare and very evpensive, indeed far outstripping in value the very cut glass it sought to imitate. Extremely rare are flip glasses, covered sugar bowls, and covered jam dishes with matching plate.