A most singular art of forming pictures with colored glass seems to have
been practiced by the ancients, which consisted in laying together
fibres of glass of various colors, fitted to each other with the utmost
exactness, so that a section across the fibres represented the object to
be painted, and then cementing them into a homogeneous mass. In some
specimens of this art which were discovered about the middle of the 18th
century, the painting has on both sides a granular appearance, and seems
to have been formed in the manner of mosaic work; but the pieces are so
accurately united, that not even with the aid of a powerful magnifying
glass can the junctures be discovered. One plate, described by
Winckelmann, exhibits a Duck of various colors, the outlines of which
are sharp and well-defined, the colors pure and vivid, and a brilliant
effect is obtained by the artist having employed in some parts an
opaque, and in others a transparent glass. The picture seems to be
continued throughout the whole thickness of the specimen, as the reverse
corresponds in the minutest points to the face; so that, were it to be
cut transversely, the same picture of the Duck would be exhibited in
every section. It is conjectured that this curious process was the first
attempt of the ancients to preserve colors by fusing them into the
internal part of glass, which was, however, but partially done, as the
surfaces have not been preserved from the action of the atmosphere.