Preliminary report on form and construction of kilns, now used for the burning of clayware / By Mr John Roe, Chief Surveyor. February 8, 1849.

  • London (England). Metropolitan Commission of Sewers.
Date:
[1849]
Catalogue details

Licence: Public Domain Mark

Credit: Preliminary report on form and construction of kilns, now used for the burning of clayware / By Mr John Roe, Chief Surveyor. February 8, 1849. Source: Wellcome Collection.

    2/16 page 2
    Class 1. The Porcelain Kiln.—The manufacture of true porcelain not having been yet naturalised in England, all examples of kilns suited to the firing of that superior ware must be taken from the Continent. Porcelain, of which the chief constituents are a white, infusible, plastic clay, called kaolin, and a felspathic flux which permeates or saturates the whole mass, requires great and long-continued heat to produce that vitreous body which charac¬ terises it. In the firing of this ware two distinct stages or operations are observed: the first is intended gradually to expel all moisture that may exist in the vessels when formed, and raise them to a red heat (in which state it is called biscuit) ; and the second is to completely bake them with the glaze or flux. The porcelain kiln of Sevres, near Paris, may be taken as an example of this class; those of Germany and other parts of the Continent differ only in the details, the general arrangement being the same in all. Figs. 1, 2 and 3 show the plan, elevation, and sections of the Sevres kiln with references to the several parts. It consists of two circular arched chambers, one over the other, for containing the ware, terminated by a wide funnel-shaped chimney. The bottom or floor of the kiln is solid and the flame is admitted to the lower chamber a little above its level; the firing-places are four in number, and the operation of firing is thus conducted:—The space occupied by each firing-place outside the main body of the kiln is filled with red-hot charcoal; the wood is then introduced in small billets from above, and the whole space completely filled ; the apertures used for stoke-hole and ash-pit are then closed, and the draught is forced to take a downward direction, and the combustion is augmented by the circumstance that all supplies of air must previously pass through the heated fuel, and thus enter in a rarefied state, producing a long and fierce flame, which is divided into three separate channels, and finds its way into the chamber through twelve narrow apertures or flues around its circumference. This lower chamber, of course, receives the greatest degree of heat, and is used for completely baking the glazed ware, which from its delicacy requires to be protected from the direct action of the fire, and for that purpose is enclosed in cases or hollow vessels of clay ware, called Seggars, fitted to each other and packed in columns (as shown in the section Fig. 3). The whole of the lower chamber is thus occupied, sufficient space only being left between the columns of ware thus packed to allow the free access of heat and flame, which afterwards finds its way through twenty-five holes in the ceiling or dome of the lower chamber into the upper one, where the unglazed or biscuit ware is placed: this of course receives a modified degree of heat and flame, and the residue passes through a smaller number of openings in its arched ceiling into the wide funnel-shaped chimney, the lower part of which is sometimes used for preparing the biscuit ware on the clay seggars or cases. The whole structure is strongly bound together by iron ties, so contrived as to allow for the expansion and contrac¬ tion consequent upon the great heat to which it is occasionally exposed. In Figs. 4 and 5 are shown a modified form of porcelain kiln recently introduced in France, and intended for the use of coal, instead of wood, as fuel. The principal
    digitised image 1
    digitised image 2
    digitised image 3