the form of protoxide. Trees and foliage have been executed in the olive tints, whilst the darker shades take their part in the borders and frets surrounding designs.
2. The Artificial Tessellæ.
These consist of red and black pottery, with the exception of the glass, to be presently described. The reds are of several tints, depending much on the nature of the clays, of which they were formed. This might have been the blue clay of different parts of the lias, in which it is known the iron is in a state of protoxide, which, on being baked in open kilns, changes to red, by becoming peroxidised, as in pottery and other clay fictilia; but the black tessellæ, as also black pottery, as so ably explained by Mr. Artis, though made from the same clay, are the result of a different method of burning; and he has clearly shown that by baking pottery in closed kilns, which he terms "smother furnaces," the carbonaceous matter of the fuel is prevented escaping. He would lead us to infer that this black smoke penetrates the ware, and thus colours it; but the real fact is that here again we have organic matter preventing the further oxidation of the iron, and besides, heightening the black by entering into combination with that metal.[1]
The employment of coloured glass in the Cirencester pavements is of rare occurrence; in only one instance has it been observed, and that under such curious circumstances as to deserve attention, if only to show that from the nature of the case it might have been in many instances overlooked.
When the medallion, dedicated to Spring—the "Flora" of the Dyer-street pavement—was exposed, a colour presented itself in the head-dress and the bunches of flowers, so different from any other that we had examined—being of a bright verdigris green—that its appearance was quite remarkable; and as the tracings were in progress, our drawing of this figure, like the rest, was rigidly imitated in the colours, as these presented them in the freshness they had when first exposed. When, however, this figure was completed, it struck me as being exceedingly inharmonious in colour and effect; we had here an olive and a verdigris green inter-
- ↑ See Mr. Artis' valuable work on "Durobrivæ," Castor in Northamptonshire, and on the remarkable kilns of the Roman potters there discovered.
