Rev. 2002-03-03, 2003-02-06
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Pressed glass involves a glob of molten glass being pushed
into a mold. The mold may be the full shape of the glass so it is
pressed flat into the mold or it may be an outline of the piece
so a plunger is pressed into the glob (forming the inside of the
piece) so it flows up against the inside of the mold - the plunger
must be shaped to pull out, so pressed glass that is not further
worked (usually the case) will always taper out. An alternative
to Pressed is Blown Mold glass where the glass is preformed on
the pipe (or on a machine) and then is placed in a mold and blown
against the walls. Blown is a uniform thickness, so the inside is dented
to match the mold, while pressed is smooth to match the plunger. Normally, the glass is further worked although
bottles and glassware may be cut and cleared by flame.
A molded piece may be created by "overblowing" into a
flat mold - a gather is worked with extra glass on the bottom and
this is placed into an open face mold and blown to press it down;
continued blowing spreads and thins the bubble till it bursts,
the edge above the mold being ground or cut after annealing. (NEGG
p.210)
Pressed glass objects that are not variations on blown objects include sun catchers, square or disk feet for goblets, paper weights or logo displays for desks.
Pressing of containers is done with an iron mold mounted in a stand with an arm across the top from which the presser hangs. Raising the arm clears the mold to add glass, the presser being placed and pushed down by the weight of the person pulling on the arm plus the leverage. In pictures the overhead arm appears to be about 6 feet off the floor. Major skill factors are having the right amount of glass put in the mold at the right temperature.
Further information on old techniques may be found in my scan of the 1911 Encyclopedia Britannica, page 97