Electrum is incorrectly translated as amber in the last edition of _Murray’s Guide_ (1893). Labarte pointed out that enamel forms the right equivalent, and for this interpretation he has ample authority. Theophilus, the Byzantine writer on the arts, continually uses the word for glass enamels, either set as separate jewels, or fused as translucent enamels to a metal base. A note in the English edition of this writer explains that this use of the word was probably extended from amber to cover other transparent bodies of similar appearance. From the lavish way in which enamel was used about the tenth century it is possible that some of the doors such as those in the iconostasis might have been enamelled. As to the “dipping” of silver or bronze with gold the Silentiary tells us that Justinian “overlaid with gold” the bronze zones of the columns; and the annulets of the porphyry columns at the east entrance still show gilding. Buzantios[372] quotes from a MS. chemical treatise in the Paris library which mentions “dipping bronze like the doors of S. Sophia,” and Fossati says the head of the Royal Door was gilt. Theophilus explains in detail how bronze or silver might be gilt by fire-gilding, the process here called dipping. The copper in the bronze had to be pure and free from lead. The gold was ground very fine and cooked with mercury. This amalgam was then applied to the surface with a copper bit, like that plumbers use in soldering, and polished with a wire brush. We have given sketches of the bronze collars which surround the columns, at the junction of capital and shaft, and just above the bases. The porphyry columns in the two western exedras have many intermediate annulets at unequal heights; these in some cases were doubtless intended to bind up longitudinal fractures in the shafts, which show in many places; but in other instances they appear to cover the junction of separate drums of porphyry. These are all shown in Grelot’s interior view. The principal collars are certainly of the time of Justinian; those under the capitals have square metal bosses or boxes covering the point where they meet and are pinned together. These “seals” of the great order bear the monograms of Justinian and Theodora. The annulets at the base are made continuous at the joint, and have the appearance of being brazed: those of the main order are now kept brightly polished. One of the base annulets in the north gallery is signed by a monogram as the work “of Stephen.”[373] Besides the hooks, in the form of upturned fingers, for the hangings at the bronze door, similar hooks occur in the marble lintels of the doors in the narthex and the exonarthex. § 2. MOSAIC.