The presentation of muffle evidence in Chapter 5 includes an alphabetical list of sites from which muffle fragments have been recovered (Table 2). This same data are presented in chronological order to highlight the sequence of development (Table 6). The data available are insufficient for firm conclusions to be drawn. The quantity of material from each site varies from single fragments to substantial quantities. A single muffle fragment can only provide evidence from its place in the muffle wall or base. Stem alignment may vary from one part of the muffle to another. Wall thickness certainly varied from rim to base and the presence of one type of buttress may not exclude that of another. Similarly the absence of a particular feature from an assemblage does not constitute proof that it was not present in the complete muffle. Despite these qualifications, developments are apparent. The tabulated data have been divided into fifty year blocks for convenient comparison. The dates in the final column being terminal dates for each assemblage, construction of the muffle is likely to have taken place earlier. As no data are available concerning the working life of a pipe kiln muffle, just how much earlier cannot be reliably estimated.
From the first half of the seventeenth century there is only one site from which muffle material has been recovered. The material from Church Field, Rainford, has a terminal date of 1650. Bases from four muffles were recovered with diameters of 360mm to 420mm. All appear to be of simple cylindrical form. Although the assemblage was large no evidence of either buttress or shelf was recovered. The fabric of the muffle has voids produced by the inclusion of organic material. The muffle wall thickness is within the range of 1045mm. This is the earliest of only two sites to produce muffle material with no pipe stem reinforcement.
The second half of the seventeenth century is better represented. There are eighteen sites operational within this period, from which muffle material has been recovered. Of these, Benthall, Gloucester, Chard, Portsmouth and Southwark have all yielded substantial assemblages. Material from all eighteen sites has pipe stem used to reinforce the fabric of the muffle. From fifteen of them organic material has also been added to the muffle fabric. Evidence for the alignment of pipe stem material within the muffle walls is far from adequate. Fragments from ten sites offer little information on this aspect. Stems are used vertically within the muffle walls at Benthall, Gloucester, and Chard; horizontally at Chard and Portsmouth; diagonally at Cambridge, Guildford, Portsmouth and Southwark. In some of the fragments from Southwark diagonal stems are reversed to form a chevron pattern. The thickness of muffle wall fragments within this period varies between 15mm and 67mm. Fragments from thickest part of the lower wall, where it joins the base, have been recovered from Benthall, Gloucester and Southwark, yielding dimensions of 55mm, 67mm and 35mm. Of the eighteen assemblages in question ten include external buttresses. From Benthall, Gloucester, Guildford, London, Portsmouth, Southwark and Staines these are prop type; from Chard and Portsmouth bar type; from Southwark also tear drop. The predominant type at this period appears to be the prop. None of the muffle wall fragments display any internal projecting feature.
Muffle material from this period includes forms which differ markedly from the mainstream evolutionary norm. The bulk of the evidence is consistent with muffles of circular plan built into updraft structures. From Gloucester, Lower Quay Street, a substantial body of muffle material is from a rectilinear form. Small fragments from Chester (Rutter & Davey 1980, 261) and Rainford (Catalogue RA1) also display sharp changes of plane inconsistent with a circular plan. The excavated material from 11 Benthall Lane (Higgins in Jones et al 1987, 5) is more heavily slagged towards the rim whilst the underside of the base is slag free raising questions concerning the fire path through the kiln. The muffles from both Gloucester and Benthall together with one other from Arcadia Buildings Southwark, were each formed with a hole through the base. These divergent forms may reflect individual experiment in the infancy of an industry with poor communications or closely guarded trade practices. The widespread use of pipe stems as reinforcement in pipe kiln muffles is, on the other hand, a powerful argument in favour of open handedness within the trade. Certainly whilst the small family-run workshop formed the basic unit of production there would be less dissemination of ideas than in latter times when journeymen plied between larger factories. In the future when more material is available it might be possible to detect regional patterns in the developments of this period and to place these seemingly aberrant structures within a logical framework.
Setting aside the difference of plan, the muffles from Benthall and Gloucester have several similarities. Both bases have an upstanding lip, at their peripheries, onto which the walls are added. In both cases the walls are reinforced with tobacco pipe stems set vertically at c. 25mm centres. Both include sparsely placed prop buttresses of unusually large dimensions. Both also have a hole through their base. Here the similarities end. The hole through the base of the Gloucester muffle is 80-100mm in diameter slagged by the passage of fire. This, together with hollow props, also displaying evidence of fire passage, suggests a tube muffle concept where in addition to passing all round the muffle, the fire passed through the interior carried in tubes or ducts to the heart of the charge. The purpose of the hole through the base of the Benthall muffle is less clear. The hole is c. 60mm in diameter and in its upper part has layers of lute extending from the inside of the muffle base. There is slight discoloration but no slagging. The underside of the base is only slightly discoloured except for radial support masking. The muffle is heavily slagged towards the rim. This is quite different from the norm where the usually unprotected base, occupying a position directly above the fire, displays heavy slagging which decreases towards the rim.
There are three possible explanations of the Benthall slagging evidence. If the fire was below the muffle, as in the majority of the pipe kilns examined, then either the muffle had some form of baffle between its base and the fire or it was inverted in use with the rim downward. The inverted scenario is unlikely due to the practical limitations this would place on loading and unloading the charge of pipes. The muffle would have to be lifted in and out of the kiln for each firing. It would be heavy, unwieldy and unforgiving in accidental contact with a stack of unfired pipes.
A baffle between the fire and the muffle would on the other hand be both easy to construct and an obvious solution to the sort of fire damage evident on the four Rainford bases. If such a baffle was constructed in the form of a shallow dish, reflecting the outer profile of the lower part of the muffle, discoloration and slagging recorded would be the natural result. Returning to the hole in the muffle base, it would certainly allow freer access for heat radiated from the baffle to the centre of the charge. This in turn might have the effect of reducing the temperature difference throughout the muffle interior thus leading to a reduction in both underfired and overfired wasters. If this scenario is correct and if the structure was successful it would be reasonable to expect later kilns to use a similar arrangement. Evidence from other sites suggests that this is not the case.
The third possible explanation of the slagging evidence is that the muffle occupied a central position in a horizontal plane between the fire and the chimney. This arrangement, termed crossdraft, is not known in any other pipe kiln context in the British Isles. Clearly further evidence from this region and period is needed before these points can be clarified.
One other structure has been examined which has a hole through the centre of the muffle base. Kiln 1 from Arcadia Buildings, Southwark, is of circular plan with a circular hole 18mm diameter in the centre of the base. This hole, which had been plugged with clay prior to the last kiln firing, clearly served a different purpose to those discussed above. It has been suggested previously (Peacey 1982, 12) that it may relate to the construction rather than the operational requirements of the kiln. It is possible that it is a socket for a vertical rod around which a line could have been rotated to check the radius of the growing structure. It is now known that at Rouen in northern France an iron rod was used in a similar position to locate and stabilise a slender column of props (chandeliers) around which the pipes were stacked. Whilst it is possible that the Southwark kiln followed a similar practice the evidence is balanced against this. No furniture was recovered from the Southwark kiln. The hole was plugged with clay prior to the last firing. The base wall thickness and the recovered wall material are consistent with a relatively short muffle. The only assemblage from this period to include items of kiln furniture is that from Gloucester where fragments from hollow props and two indented buns were recovered.
From the first half of the eighteenth century there are thirteen pipe kiln assemblages which include muffle material. Two of these are large enough to be considered as representative. These are Aylesbury, with a terminal date of 1710, and St Albans, with a terminal date of 1750. Muffle material from all thirteen sites has pipe stem used to reinforce the fabric together with voiding from organic filler. Stem alignment in the muffles from Aylesbury and Helston is in reversed diagonal bands to form a chevron pattern. Diagonal stemming is recorded from Guilford, Exeter and St Albans; horizontal stemming from Chelmsford and vertical from Exeter. The maximum wall thickness recorded in this period is 60mm. Prop buttresses are recorded from Aylesbury, Chelmsford, Guilford, Helston, Exeter and St Albans. From Aylesbury also tear drop buttresses. There is no evidence from this period for any internal shelving. Of the thirteen assemblages only that from Chelmsford includes furniture. This one case is a prop with a cruciform arrangement of stems at its upper extremity eminently suitable to form the support for a conical stack of pipes. The design of the prop top precludes the possibility of a stacking column.
From the second half of the eighteenth century there are sixteen recorded assemblages which include muffle material. The quality of these groups is generally poor, the Waterford kilns providing the only substantial assemblages. In all cases stems are used to reinforce the muffle fabric. Stem alignment can be ascertained in only four of these. The material from Southwark 2 has diagonal stems; from Bristol 1 horizontal and from the three Waterford kiln groups a combination of horizontal and vertical. In the material from seven sites voids from organic filler are clearly visible. The maximum wall thickness recorded is 100mm from Waterford. Bar type buttressing appears to have replaced the props of earlier periods being recorded from Brentford 2, Bristol 1, Rainford 10 and the three Waterford groups. Two sites have produced peripheral shelf fragments: from Bristol there is a cornice type and from Waterford a wall step. The peripheral shelf-tiered structure had clearly evolved by the end of the century.
From the first half of the nineteenth century there are twenty assemblages which include muffle material. In all of these stems are used within the muffle fabric. In the eight cases where alignment is certain the stems are horizontal. At Southampton 2 stems occur horizontally and diagonally in separate fragments. In material from fifteen groups there is obvious organic voiding. The maximum wall thickness is 110mm. Bar type buttresses are recorded from Leicester, Canterbury, Bristol, Ipswich, Southampton, Chatham, Northampton and Winchester. From Rainford there is a single prop type buttress. From seven sites shelf fragments are recorded; step type from Bristol 10 and Canterbury; cornice type from Southampton and Northampton; step and cornice from Bristol 5, Bristol 7 and Winchester.
There are ten assemblages from the later half of the nineteenth century which include muffle fragments. In all cases stems have been used in the muffle matrix. Seven also exhibit voids consistent with included organic matter. In the five instances where stem alignment is obvious it is horizontal. The maximum wall thickness recorded in this period is 60mm. In the six instances of recovered buttress data it is of bar type. Six assemblages also included shelf material, five of cornice type and one of step type.
Only a relatively small number of factories survived into the twentieth century. Muffle material has been recovered from three of these, namely Boston, Nantgarw and Leeds. The single large fragment recovered from the surface at Nantgarw probably dates from the first half of the nineteenth century as it is known that in the latter half pipes were fired in a large double chambered bottle kiln (Williams 1932, 110-11). This fragment has both step type peripheral shelf and bar type buttress. It has included stem and organic voiding. The greater wall thickness is 75mm. The Boston fragment is also of probable nineteenth century date. It is a bar type buttress with both included stem and organic voiding. There is no measurable wall. The Kiln from Leeds was in use until 1950. It was later moved to Kirkstall Abbey Museum where it forms part of a permanently displayed pipemakers workshop. This muffle is constructed from fire bricks with the peripheral shelves pegged into the joints. This method of construction was previously postulated from archaeological evidence recovered in Gloucester (Peacey 1979, 725). The wicket of an earlier muffle from Lewes, built in the conventional manner from clay reinforced with pipe stems, was built up for firing with brick or tile. Wadding and pegged shelving recovered from this kiln is indistinguishable from that resulting from a structure built entirely of bricks or bats. It is now thought more probable that the Gloucester material represents a wicket infill rather than a brick built muffle.
It can now be observed from the collected data that the presence of pipe stem reinforcing and the inclusion of organic matter within the muffle matrix were widespread practices throughout the study area, of neither geographical or chronological significance. Although stem alignment is of some chronological significance its interpretation has to be tempered with additional factors. As a broad generality stem alignments changed from predominantly vertical and diagonal up to the middle of the eighteenth century to predominantly horizontal thereafter. Maximum wall thicknesses increased at some time during the eighteenth century coincidental with an increase in muffle height and introduction of peripheral shelves. The type of buttressing also underwent a change in this century from predominantly prop to predominantly bar. In the event of recovering an isolated muffle fragment from an unstratified context it would only be possible to say that it is either earlier or later than c. 1750 by reference to its combined features.
Clearly the insertion of pipe stems into the muffle wall ensured its ability to withstand the otherwise terminal effect of severe cracking. Repairs could be made easily either by insertion of new pieces, application of patches and luting over the inner surface. Encased and supported within a brick shell this type of muffle was clearly able to function for a great number of firings, more likely measured in years rather than weeks or months. There is evidence that such a muffle was of sufficient durability and value that it might be removed to another site if circumstances required. From Rainford conditions of sale by public auction on 24th December 1849, of property owned by Thomas Woods, by excluding certain items imply the intention to remove them:
The two pots and Kilnes the Racks Trough Block and other Tools in the Pipe Shop and the Boston hay rack and manger in the Cart Shed are hereby excepted (Dagnall 1992, 8).
In this context it seems likely that the two pots referred to are muffles. As can be seen in the account of McLardy's Manchester kilns his muffle kilns were called potkilns. A similar record of kiln lining removal appears in the sale particulars of The Eagle public house at Leighton Buzzard (which included rooms used as a Pipe Manufactory). The sale was scheduled for 4th July 1893.
The vendor also reserves the right to remove the inner casing of the pipe kiln (Bedfordshire Record Office BML 10/42/96).Whilst this could of course refer to a fire-brick lining, evidence discussed below suggests that the smaller pipe making establishments such as this continued to use muffle kilns into the twentieth century. That the casing referred to was in fact a muffle cannot be ruled out.
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