A few small specimens of Roman Glass have
been preserved in the British Museum. One of them was of an octagon
form, of light azure blue, which crumbled to fragments on being exposed
to the air and light; it had a dull appearance, and the crumbling
of the particles without friction, was caused by an excess of alkali,
gradually exuding for many years, until the cohesion of the crystals
was destroyed. Trade secrets in the preparation of Glass for gems*
most likely existed in ancient times; for very little has been written
by Egyptians, Greek, or Roman authors on the chemical constituents of
Glass gems, or cameo-engraved vases. Glass in solid pieces, such as
gems and mosaics, was, probably, manufactured in small Glass-houses;
and the trade secrets of the processes may have passed from father to
son for several successive generations. The Glass-makers of Rome had
a street assigned them in the first region of the city. A tax was,
also, laid upon them by Alexander Severus, which existed in the time of
Aurelius, and probably long after.†
Glass-making in Britain is supposed to be
of very ancient date; if the opinion of Pennant be well founded, of a
period prior to the Norman Conquest. The art of manufacturing Glass into
such ornaments as beads and amulets, was certainly known to the
Druids; and Glass vessels were made by the
Glass of the usual density, is about 3.200 to 1.000 of water.
Subsequently, other pieces of Glass have been exhumed in the city of
London; these are considered, by Mr. Roach Smith, to be ancient Roman;
one small piece is of 2.600, and another 3.144, specific gravity.
(See remarks in the after part of this work.)
† A sort of ancient excise,
highly injurious to industrial art, and, probably, one of the causes
that transferred the Glass manufacture to Venice.
‡ See sketch and description
of an Anglo-Saxon vase, in No. 8, page 347, of the Journal of the
British Archæological Association.