Figure 17: Sketch based on the Bristol, Waverly Street evidence.
The type example for the developed muffle in widespread use by the early nineteenth century is that from Waverly Street, Bristol (Peacey 1982, 10-13). It is similar in most respects to those described by Good 1813 and Rees 1819 in the early nineteenth century. The base is missing from the Waverly Street assemblage, though two fragments from the lower wall (Not illustrated), dishing inwards on the inner profile have the imprint of upright bowls in the lower fracture. The lowest stage in the wall is notably thicker than those above and at the point where the thickness is reduced the step formed acts as a shelf. The wall above this point reduces gradually in thickness and subsequent shelves project inwards from it. Pipe stems are included within the wall concentrically in horizontal layers up to the penultimate shelf. From this point upwards, the wall being much thinner, rings of single stems sit one upon another sandwiched within the wall. The shelves are added to and pegged to the inner surface of the muffle with horizontal radial pipe stems. There is an opening in the side, angled from the rim to the top shelf, through which it passes, appearing to continue vertically downwards from that point. The buttresses are in the form of vertical bars with apertures, apparently square cut, through them at intervals. Numerous pipe stems are included, arranged in a haphazard fashion, aligned vertically within the bars. The flue space surrounding the muffle tapers from c. 100mm to c. 50mm.
A substantially complete assemblage from a muffle of similar date was recovered from Temple Backs, Bristol in 1983. After demolition the muffle fragments had been deposited in brick-arched bunkers. At some later date a service trench had been cut through the deposit and many of the up-cast fragments were then used to build a wall. Before any complete appraisal of this unique assemblage can be made a good deal of cleaning and conservation is required. Preliminary recording and examination has revealed many structural nuances. The muffle appears to have been built within a cylindrical brick structure. The muffle buttresses are of bar type, bridging a flue space which tapered from c. 110mm at the base to c. 30mm at the rim. If the outer wall of the kiln was vertical, this narrowing flue space would result in a muffle wider at its rim than at its base. This widening would be exaggerated on the inside due to the reduction in wall thickness from c. 100mm at the base to c. 30mm at the rim. The base itself is formed of a flat disc c. 50mm thick reinforced with clay tobacco pipes; stems radiating from the centre and bowls arranged alternately to form a double row within the base of the first wall stage. At the top of this stage the wall reduces in thickness, the resultant step forming the first shelf (Figure 16). This first stage measures 245mm in height. Although the height of the second stage is not yet known, this too ends in a step shelf as the wall thickness again reduces. From this point to the rim it appears that the wall thickness reduces gradually, all further shelves being pegged into and projecting inwards from the inner surface of the wall. The distance between shelves on the stage, including the lower edge of the door, measures 260mm and from the final shelf to the rim is 240mm. The arrangement of pipe stems within the walls is similar to the Waverly Street example; horizontal layers of concentric bands of stems in the thicker wall sections reducing to layers, each of a single band in the thinner sections. The rim is of rounded profile giving no clue as to either permanent or temporary cover. The buttresses around the outside appear to be continuous, from rim to base with no interconnecting flues. The only recognisable terminals are at the rim, where they are of rounded profile, and c. 140mm above the base, where they are groined. They are spaced at c. 210mm intervals. The door opening is of 'keyhole' design, wider at the top than the bottom. The lower part spanned at least two flue spaces; a minimum width of c. 420mm. One fragment of the lower edge includes a buttress terminal. The sides of the door follow the edges of buttresses rising vertically through one shelf for a distance of c. 275mm to a shoulder. Although the shape beyond this point has not yet been established it evidently widened before rising to the rim. There is clearly a good deal more information to be gleaned from this assemblage by cleaning and organising the fragments relative to one another. Because of the weight involved, actual physical reconstruction is probably impractical. However, if the fragments were organised as if the muffle had been cut vertically and unrolled onto a flat surface, it is probable that full details of all structural features would be revealed.
Internal projecting shelves of cornice type are recorded from Bristol, Gloucester, Lewes, Manchester, Northampton, Southampton, Waterford and Winchester. Shelves formed by a step reduction in the wall thickness are recorded from Bristol, Canterbury, Gloucester, Nantgarw, and Winchester; possibly also from Manchester and Waterford.
The kiln removed from Samson Strong's Cottage Street works at Leeds features a muffle built from commercial fire-bricks set end upon end to form a cylindrical chamber. The four peripheral shelves are pegged into every second joint resulting in a vertical separation of c. 450mm. The internal diameter of the muffle is 1189mm. The muffle wall is 70mm thick. The flue space surrounding the muffle is 100mm across. There is a fire-brick lining to an outer shell of red brick, each being 120mm thick. In its reconstructed form, the muffle base is raised 100mm above the floor of the chamber on a number of brick supports. Three fireboxes are built on the outside of the kiln shell with their throats, each of 230 square centimetres, discharging at the base of the muffle. No notes, drawings or photographs of the kiln in its original location are known to exist. The fireboxes contain no grates. The throats are not original brickwork. There must be a question mark, therefore, over the accuracy of the reconstruction.
Fragments of peripheral shelf pegged into a clay joint with the clear impressions left by surrounding bricks or tiles have been recorded from Gloucester, 99 Westgate Street (Peacey 1979, 72-5), and Lewes, Pipe Passage. The Lewes examples are accompanied by matching tiles, one of which includes a spy hole. The Lewes assemblage also includes traditional pipe-reinforced muffle wall fragments with bar buttresses and peripheral shelving. This combination suggests that the tiles and their shelves are from the wicket. The Gloucester assemblage is much smaller and possibly less representative of the complete structure. In it there is no pipe-reinforced muffle material. Although it is possible that the entire muffle was constructed along similar lines to that at Leeds (from brick or tile with pegged shelving), a wicket origin for the recovered material cannot be ruled out. Fragments of peripheral shelves from Northampton, Chalk Lane, display a flat interface with the muffle wall with no stem pegging. The life of such a joint would be limited, suggesting that these might come from a brick- or tile-filled wicket which, by definition, has a life of one firing only.