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.