A HISTORY OF NORTHAMPTONSHIRE It has however been suggested that the dark colour is not due merely, as Mr. Artis supposed, to a ' colouring exhalation ' permeating the articles, but to a distinct chemical action set up by the carbonaceous vapour of which the smothered kiln would be full. The point is one rather for a chemist or a potter than an archae- ologist, and I may be permitted to leave it unsettled.^ Arrangements for glazing were also met with (fig. 31) : — In the course of my excavations, I discovered a curiously-constructed furnace, Fic. 31. Glazing Furnace. of which I have never before or since met with an example. Over it had been placed two circular earthen fire vessels (or cauldrons) ; that next above the furnace was a third less than the other, which would hold about eight gallons. The fire passed partly under both of them, the smoke escaping by a smoothly-plastered flue, from seven to eight inches wide. The vessels were suspended by the rims fitting into a circular groove or rabbet, formed for the purpose. The composition of the vessels was that of a clay tempered with penny-earth. They contained some perfect vessels and many fragments. It is probable they had covers, and I am inclined to think were used for glazing peculiar kinds of the immense quantities of ornamented ware made in this district. Its contiguity to one of the workshops in which the glaze (oxide of iron) and some other pigments were found, confirms this opinion. Mr. Artis calls the glaze an oxide of iron. The British Museum and the Jermyn Street Museum of Geology possess cakes of vitreous matter found by Mr. Artis at Castor which was probably used as a glaze, and which consists principally of silicates of soda and lime.' Finally, with respect to the ' barbotine ' ornamentation in slip : — The vessel, after being thrown upon the wheel, would be allowed to become somewhat firm, but only suflBciently for the purpose of the lathe. In the indented ware the indenting would have to be performed with the vessel in as pliable a state as it could be taken from the lathe. A thick slip of the same body would then be procured, and the ornamenter would then proceed by dipping the thumb or a round mounted instrument into the slip. The vessels, on which are displayed a variety of hunting subjects, representations of fishes, scrolls and human figures were all glazed after the figures were laid on ; where however the decorations are white the vessels were glazed before the ornaments were added. Ornamenting with figures of animals was effected by means of sharp and blunt skewer instruments, and a slip of suitable consistency. These instruments seem to have been of two kinds : one thick enough to carry sufficient slip for the nose, neck, body and front thigh ; the other of a more delicate kind, for a thinner slip for the tongue, lower jaws, eye, fore and hind legs and tail. There seems to have been no retouching after the slip trailed from the instru- ment. Such are the chief features of the typical Castor ware as we know it from specimens found in and near the Castor kilns, and such appear to be the general methods of its manufacture. It is not however con- ' Buckman and Newmarch, Remains of Roman Art in Cirencester, pp. 77-8. • An analysis made by Sir Hy. de la Beche, late keeper of the Jermyn Street Museum of Practical Geology, gives : Silica, 69-4.0 ; soda, I4'63 ; lime, 7'8l ; alumina, 2"62 ; with traces of protoxide of iron, protoxide of manganese, magnesia, potash and carbonic acid. 210
