Of ancient glass probably the best-known example in the world is the Portland Vase in the British Museum; this is composed of a layer of white glass over blue glass, the outer coating skilfully cut into a pattern. More ordinary types of glass dating to Roman times are in the form of small bottles, often called 'Tear Bottles', which have been excavated and as a result of lengthy burial are covered in iridescence. The Romans mastered the art of making glass of all the types known in later years, and subsequent techniques have been rediscoveries. Considering the centuries that have passed and the delicacy of the material a considerable number of fine specimens has survived, but they are to be seen rarely outside museums.
Following the fall of the Roman Empire, the art of glass-making suffered a decline, but in
Persia and other countries of the Near East some good pieces were made between the seventh
and eleventh centuries. Later, in Syria some highly decorated articles, notably vases and
mosque-lamps, were made and specimens of these outstanding works may be seen in the
principal museums. At the same time, in Europe low bowls and cups were being made from a
greenish or brownish coloured glass. A peculiarity of these is that the fitting of a foot
to the articles, common enough in Roman times, seldom seems to occur; it would appear that
the arts of making a foot and joining it to a vessel had been forgotten.