3. ROMAN POTTERY-FURNACES

The remains of pottery-kilns and furnaces discovered in various parts of Europe have furnished a considerable amount of valuable information on the system employed in baking the vases. On this particular point, indeed, we know far more in regard to Roman pottery than to Greek, although, as we have seen in Chapter V., the painted vases themselves sometimes yield information on the appearance and arrangement of the furnaces. But remains of actual furnaces have been found in many places in Western Europe, notably in Germany, France, and Britain, in a more or less complete state, as also in Italy, at Pompeii, Modena, and Marzabotto.[3122] A complete list of those known in 1863 has been given by Von Hefner,[3123] supplemented by Blanchet’s lists of furnaces found in France (1898 and 1902).[3124] In Gaul the best examples are at Lezoux, near Clermont, at Châtelet in Haute-Marne,[3125] and at Belle-Vue, near Agen, in the Department of Lot-et-Garonne.[3126] The latter was circular in form, below the level of the soil. In Germany important remains have been found at Heiligenberg in Baden, Heddernheim near Frankfort, Rheinzabern near Karlsruhe, and Westerndorf.[3127] All these in general arrangement differ little from those in use at the present day; the Heddernheim furnace (Fig. 212) was found in the most perfect preservation, but was subsequently destroyed, not, however, before satisfactory plans and drawings had been made.[3128] In Britain by far the most important discoveries have been made at Castor, Chesterton, and Wansford in Northants, where the remains extend for some distance along the Nene valley.[3129] They were first explored by Artis in 1821-27, who published a magnificent series of plates in illustration, entitled _Durobrivae_; these he supplemented by a full description in the _Journal_ of the British Archaeological Association.[3130] Castor and Chesterton (the latter in Hunts) are both on the site of Roman towns, and were the centres of a special local ware, described in a succeeding chapter. The potteries, being so numerous, are probably not all of the same age. [Illustration: FIG. 212. ROMAN KILN FOUND AT HEDDERNHEIM, GERMANY.] In 1677 four Roman kilns were discovered in digging under St. Paul’s Cathedral for the foundation of Sir C. Wren’s building, at a depth of 26 feet. They were made of loam, which had been converted into brick by the action of the fires, and were full of coarse pots and dishes; they measured 5 feet each way. A drawing made at the time is preserved among the Sloane MSS. in the British Museum.[3131] In the kilns was found pottery of the kind typical of London and the neighbourhood. In 1898 two kilns, one of large size, with pottery bearing the name CASTVS FECIT, were found near Radlett in Herts,[3132] and another was excavated in 1895 by Mr. C. H. Read at Shoeburyness.[3133] In Norfolk a kiln of somewhat curious form was found in the Roman settlement of Caistor by Norwich; the shape is that of a shallow concave depression with partitions, and it contained vases placed ready for baking.[3134] Another found between Buxton and Brampton was recorded by Sir Thomas Browne,[3135] and a third at Weybourne.[3136] In the South of England kilns have been found in the New Forest, where there was a manufacture of local pottery[3137]; in Alice Holt Forest near Petersfield, Hants; at Shepton Mallet in Somerset; and a potter’s workshop at Milton Abbas, Dorset.[3138] The British Museum contains a model of a kiln unearthed at Worcester about forty years ago, on the site of the modern porcelain works. Finally, discoveries of kilns and pottery were made in 1819 at Colchester, and again in 1878, when five kilns, all of different forms, with local pottery, came to light.[3139] To describe all these different types of furnaces in detail would of course be impossible, but much may be learnt from the very full, though now somewhat antiquated, descriptions of the Castor kilns given by Artis.[3140] It will be found more satisfactory to describe the generally-prevailing arrangements, noting the more important variations where they occur. It may further be laid down that the system was practically the same for terracotta figures and tiles as for pottery, and that in many cases both were made in the same furnace. But this was not invariably the case, and at Rheinzabern, for instance, the kilns for tiles were quadrangular, those for pottery circular. The kilns were constructed partly of burnt, partly of unburnt brick, the interior, floor, and outside of the roofs being covered with a strong layer of cement. They consisted of two main portions, the fire-chamber with its adjuncts, and the vaulted chamber above, in which the objects to be baked are placed. The fire-chamber was usually circular, with a projection in front, the _praefurnium_[3141] which had either a vaulted roof, as at Castor and Heiligenberg, or a gabled roof formed of pairs of tiles, as at Rheinzabern. Through this the fuel was introduced, consisting chiefly, as charcoal remains show, of pine-wood. The fire-chamber was either divided up, as at Castor, by walls radiating from a central pillar which supported the roof, or by rows of pillars in a line with the entrance, as at Rheinzabern and Heiligenberg. Holes were bored in the roof to allow the heat to penetrate through, but the arrangement varies; at Heiligenberg each division of the furnace was vaulted, making grooves along which the holes were bored. The oven where the pots were placed has been destroyed in most cases, but we know that it consisted of a floor, a wall with entrances, and a vaulted dome. The pots were ranged partly on the floor, partly on terracotta stands over the holes, as at Rheinzabern and Heiligenberg[3142]; at Lezoux there are remains of holes in the walls for iron bars to support them. Special arrangements seem to have been made for baking the finer wares, in order to ensure the proper spread of heat, and to guard against their being blackened or otherwise injured. In the Romano-British Room of the British Museum is a lump of bowls of red ware from Lezoux, fused together in the baking and cast aside.[3143] One of the kilns at Castor (Fig. 213) is described by Artis as a circular hole 3 to 4 feet deep and 4 feet in diameter, walled round to a height of 2 feet; the _praefurnium_ was about a foot in length. In the centre of the circular hole was an oval pedestal (with one end pointing to the furnace-mouth), on which and on the side wall the floor was supported, being formed of perforated angular bricks meeting in the centre. The vaulted dome was composed of bricks moulded for the purpose,[3144] and the sides of the kiln of curved bricks set edgeways in a thick slip of the same material. Brongniart[3145] compares the Castor kiln with that at Heiligenberg, near Strasburg, and others in the Rhine valley in which “Samian” ware was made. [Illustration: FIG. 213. KILN FOUND AT CASTOR, NORTHANTS.] Another kiln found in 1844 Artis describes as having been “used for firing the common blue or slate-coloured pottery, and had been built on part of the site of one of the same kind, and within a yard and a half of one that had been constructed for firing pottery of a different description. The older exhausted kiln ... presented the appearance of very early work; the bricks had evidently been modelled with the hand, and not moulded, and the workmanship was altogether inferior to that of the others, which were also in a very mutilated state; but the character of the work, the bricks, the mouths of the furnaces, and the oval pedestals which supported the floors of the kilns, were still apparent.” Artis was also of opinion that “the blue and slate-coloured vessels found here in such abundance were coloured by suffocating the fire of the kiln, at a time when its contents had acquired a degree of heat sufficient to ensure uniformity of colour.” Hence he denominated kilns in which this ware was baked, “smother kilns.” He further notes that the bricks of this kiln “were made of clay mixed with rye in the chaff, which being consumed by the fire [_i.e._ in the baking of the bricks] left cavities in the room of the grains, which might have been intended to modify expansion and contraction, as well as to assist the gradual distribution of the colouring vapour. The mouth of the furnace and top of the kiln were no doubt stopped; thus every part of the kiln was penetrated with the colouring exhalation.” From experiments made on the local clays he proved to his own satisfaction that the colour could not have been produced by any metallic oxide, inherent or applied from without; and this view was supported by the appearance of the clay wrappers of the dome of the kiln. But in view of recent researches, such as those of Blümner, it is doubtful whether Artis’ theories can now be upheld. As Mr. Haverfield has pointed out,[3146] the dark colour may be due to the chemical action of the carbonaceous vapour of the smothered kiln rather than to any “colouring exhalation.” The process of packing the kiln in order to secure uniform heat in firing is thus described by the same writer: “The kilns 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 on the grass upon the vessels; he then placed more grass on the edge of the clay just laid on, and 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 the last layer of plaster, until he had reached the top, in which a small aperture was left, and the clay nipt round the edge; another coating would be laid on as before described. Gravel or loam was then thrown up against the side wall where the clay wrappers were commenced, probably to secure the bricks and the clay coating. In consequence of the care taken to place grass between the edges of the wrappers, they could be unpacked in the same-sized pieces as when laid on in a plastic state, and thus the danger in breaking the coat to obtain the contents of the kiln could be obviated.” In the course of his excavations Artis discovered a singular furnace,[3147] “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.” He was strongly of opinion that this furnace was used for producing glazed wares by means of iron oxide. Whether this is so or not, it is interesting to note that in the British Museum and Museum of Geology there are cakes of vitreous matter from Castor, probably used as a glaze, and consisting of silicates of soda and lime.[3148] The kiln found at Caistor, in Norfolk, was apparently used for baking the grey Roman ware, and differed in form from those described, which were for the black, being only calculated for a slight degree of baking. It was a regular oval, measuring 6 feet 4 inches in breadth. The furnace holes were filled in below with burnt earth of a red colour, and in the upper part with peat; the exterior was formed of strong blue clay of 6 inches in thickness, and the interior lined with peat; the kiln was intersected by partitions of blue clay. Some of the vases were inverted and filled with a core of white sand.[3149] [Illustration: FIG. 214. PLAN OF KILN AT HEILIGENBERG.] The furnaces at Heiligenberg and Rheinzabern present the following further peculiarities.[3150] The former, which were evidently used for the baking of red wares, had a flue in the form of a long channel with arched vault, the mouth being over 8 feet from the space where the flames and heat were concentrated under the oven (Fig. 214). Numerous pipes of terracotta, of varying diameter, diverged from the upper part or floor of the oven, to distribute the heat; in the outer wall of the oven was a series of smaller ones, and twelve or fifteen of larger size opened under the floor of the oven to distribute the heat and flame round the pots (Fig. 215). The mouths of the pipes were sometimes stopped with baked clay stoppers to moderate the heat. The upper part or dome of the kiln is never found entire, having been generally destroyed here, as elsewhere, by the superincumbent earth. Walls of strong masonry separated and protected the space between the mouth of the flue and the walls of the oven, and the floor of the latter was made of terracotta tiles. [Illustration: FIG. 215. SECTION OF KILN AT HEILIGENBERG.] At Rheinzabern, where excavations were made in 1858, fifteen furnaces were found, some round and others square, but all constructed on the same plan. The floor of the oven was over 3 feet below the top of the walls, and was covered with tiling, the walls being formed of rough slabs of clay, about 28 by 16 inches in size. The floors of the ovens were in some cases supported by bricks covered with a coating of clay. Stands of baked clay in the shape of flattened cylinders supported the pots in the oven, and these rested on pads of a peculiar form, roughly modelled in clay.[3151] In all, seventy-seven pottery-kilns and thirty-six tile-kilns were discovered on this site.[3152] The following list, though by no means claiming to be exhaustive, gives the names of the chief potteries where actual furnaces have been discovered.