But plates of glass, somewhat similarly decorated, may play an even more important part in the decoration of the backs of altars, especially on the spandrels in the lower arcades of the reredos. The decoration now becomes pictorial, and is often most carefully executed. Or, again, such a little glass picture may be detached and mounted in a frame to form a pax or _baiser-de-paix_, a _bijou_ reliquary, or other small devotional object. In such cases the gold is applied to the back of the glass by weak gum, and the design traced with a pointed instrument somewhat in the manner of the catacomb glasses. The effect may be heightened in various ways by additional touches of pigment on the draperies, or by a glazing of colour for the flesh-tints; the colours are worked up with a resinous body, and silver foil in little plates and spangles is added in places; finally, over the back is laid a piece of tinfoil, and this is folded over the edges (M. Alfred André, quoted by M. Molinier, _Spitzer Catalogue_, vol. iii. p. 54). The back of the plate is generally found to be protected by a kind of pitchy varnish; to fix this some application of heat was doubtless necessary, but in no case, I think, is the gold design in this late mediæval work enclosed between pieces of glass which have been subsequently fused together.[103] We are here concerned only with the Gothic examples of this class of work, and of these the majority appear to come from the north of Italy—they are probably of Milanese or Venetian origin. There is often in these early Italian plaques a coloured backing under the gold, generally of a bright red, but sometimes of green or black, and this backing shows through in places. In the case of a very beautiful example formerly in the Spitzer collection, the design was drawn upon the central portion of a plate of flashed glass; although this medallion is only 5-1/2 inches in diameter, there is a distinct boss in the centre. That such a defective piece should have been chosen for this delicate work would go to prove the rarity of sheets of glass with even surface at this time. In later days more colour was used in the decoration, but such work as the magnificent _baiser-de-paix_ in the Louvre, which came from the chapel of the order of the St. Esprit, does not fall within our present limit of time. The late Marquis Emanuele D’Azeglio devoted himself to collecting specimens of gilt and painted glass of all ages and countries. This collection, unique of its kind, he bequeathed to his native town of Turin, where it is now exhibited in the Museo Civico. In some of the earlier pieces, especially on one of Byzantine character—perhaps Muranese work of the end of the thirteenth century—the gold is laid down upon glass of very irregular thickness. There are a few examples of Gothic work of this character in the British Museum, at South Kensington, and in the collection of Mr. Salting. CHAPTER IX