The researches further proved that the colour could not be attributed to any metallic oxide (although it must be confessed that in many instances the surface has a strongly developed metallic appearance) either in the clay itself or applied externally, and this conclusion is confirmed by the appearance of the clay wrappers of the dome of the kilns; and it may be added, the colour is so fugitive that it is expelled entirely, by submitting the pottery to an open fire. During the examination of the Upchurch pottery, Mr. Artis remarked that he thought a coarse kind of sedge had been used in the manufactory. His practical eye alone guided him to this conclusion, for he had never visited the site, and was quite unaware that below the strata of broken vessels, a layer of sedge peat is in several places visible. The same kind of arrangement probably obtained pretty generally with the Roman potters. [Illustration: Fig. 100.--Potter’s Kiln, Normangate Field, Castor.] [Illustration: Fig. 101.--Potter’s Kiln, Normangate Field, Castor.] The kilns for firing the Castor ware, discovered by Mr. Artis, are among the most interesting of all the remains of Roman arts which have been brought to light. The kilns which were removed in the course of the investigations were “all constituted on the same principle: a circular hole was dug from three to four feet deep, and four in diameter, and walled round to the height of two feet. A furnace, one-third of the kiln in length, communicated with the side. In the centre of the circle so formed was an oval pedestal, the height of the sides, with the end pointing to the mouth of the furnace. Upon this pedestal and side walls the floor of the kiln rests. It was formed of perforated angular bricks, meeting at one point in the centre; the furnace was arched with bricks, moulded for the purpose; the side of the kiln was constructed with curved bricks set edgeways (see Fig. 100) in a thick slip (the same material made into a thin mortar) to the height of two feet. The process of packing the vessels and securing uniform heat in firing the ware was the same in the two different kinds of kilns--namely, that before described, called ‘smother kiln,’ and that for various other kinds of pottery. They were first carefully loose-packed with the articles to be fired, up to the height of the side walls. The circumference of the bulk was then gradually diminished, and finished in the shape of a dome. As this arrangement progressed, an attendant seems to have followed the packer, and thinly covered a layer of pots with coarse hay or grass. He then took some thin clay, the size of his hand, and laid it flat over the grass upon the vessels: he then placed more grass on the edge of the clay just laid on--then more clay--and so on until he had completed the circle. By this time the packer would have raised another tier of pots, the plasterer following as before, hanging the grass over the top edge of