How far the so-called _diatretum_ work is based upon such _appliqué_ or added portions of glass is a much disputed point. Mr. Nesbitt appears to have regarded all such work as so formed (_Catalogue, Slade Collection_, pp. xiv.-xv.), and the imitations now made at Murano are certainly built up in this way; not so, however, some of the genuine ancient pieces, I think. (See below, p. 71.) Footnote 35: The Egyptians, too, as we have seen, sometimes decorated their glass with similar splashes, but we never find that these are distorted. Footnote 36: There are many allusions to the painting of glass, in some cases merely by varnishes, in the early mediæval treatises on glass (see Chap. VII.). Some of these recipes, as we shall see, may have been handed down from classical times. Footnote 37: The contents have been described by the late Canonico Passini, in a magnificent work published by Ongania of Venice, in which nearly every piece of importance is reproduced in colour or by photography. Footnote 38: There is among the Roman glass in the museum at Cologne a shallow bowl about a foot in diameter, painted on the back, as in the later _verre églomisé_, with a female head. The colours—black, red, and white—are but slightly burnt in, and therefore much decomposed. Footnote 39: This part is stated to be a distinct piece cemented on to the bottom of the vessel. So at least says Mr. Apsley Pellatt in his _Curiosities of Glass-making_, writing, I think, before the vase was broken. In the same book will be found a careful account of the process of ‘casing’ as now practised. It was probably by some such plan, in the case of the Portland vase, that the _paraison_ of blue glass was blown into the previously prepared vessel of opaque white. Footnote 40: I shall return to this sculptured work when treating of Byzantine glass in the next chapter. Footnote 41: By the courtesy of Lord Rothschild I have had an opportunity of examining this wonderful cup. It is undoubtedly carved from one piece of glass. The spirited execution would seem to point to a date hardly much later than the beginning of the third century. The internal depressions were made perhaps with the object of lighting up the external figures. The glass by transmitted light is of a fiery red, tending to purple, but the figure of Lycurgus is exceptionally of a fine amethystine tint. I think that in both cases the colour is probably due to a skilful use of manganese. Footnote 42: The abrading material employed along with the wheel was probably in most cases corundum or emery (the _adamas_ of the ancients) in a powdered form; not the diamond, which was excessively rare, nor the emerald, as is sometimes stated. This last stone is not only much rarer than corundum, but it is also not so hard. Footnote 43: Compare what is said below on p. 82 of Greek-speaking Syrian artisans. Footnote 44: