184a'] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL 



14.5 



PORCELAIN KILN. 



Alfred Vincent Newton, of the Oifice for Patents, 66, Clian- 

 cery-lane, Middlesex, mechanical draughtsman, for " an invention 

 of an improved kiln (ir oven, for firing porcelain and other similar ware." 

 (A communication.) — Granted July 29, 1847 ; Enrolled January 

 29, 1848. [Reported in Newton's London Journal.'] 



The inventor, in order to explain more fully the nature of his 

 improvements, has prefaced his specification with the following ob- 

 servations, explanatory of the ordinary mode of firing or baking 

 hard porcelain, and the difficulties and objections incident thereto. 



The employment of pit-coal as a fuel for firing or baking hard 

 porcelain has hitherto been thought impossible, or at least subject 

 to almost insuperable difficulties. It was thought that the hard- 

 ness and infusibility of the clay (kaolin), and the liigh degree of 

 heat necessary to fuse or melt the glaze whicli is employed to cover 

 hard porcelain, were insurmountable obstacles. A long and suffi- 

 ciently large or extensive flame to occupy the whole space of the 

 oven or kiln is indispensable for this kind of manufacture ; and 

 the liability of the matters composing the hard porcelain to become 

 discoloured, rendered this superabundance of flame the more ne- 

 cessary, in order that no smoke might be allowed to remain in the 

 kiln or oven. It is requisite, therefore, to cause pit-coal to develope 

 such an amount of flame as would have the same effect, and would 

 act within a given time in the same manner as wood. 



The matters of which hard porcelain is composed, are divided 

 into two classes, — first, the paste or clay, which is a principal ele- 

 ment ; and second, the glazing or enamelled covering. The paste 

 or clay consists essentially of two elements ; the one is an infusible 

 argillaceous matter, — this is kaolin, either alone or mixed with 

 plastic clay, or with magnesite, — the other, arid and infusible, is 

 given by felspar or other stony minerals, such as siliceous sand, 

 chalk, or gypsum, either separately or mixed together in difl^erent 

 combinations. The enamel or glaze consists of quartzoze felspar, 

 sometimes alone and sometimes in combination with gypsum, but 

 always without either lead or tin. Hard porcelain must, in fact, 

 be considered as hard compact impermeable pottery-ware, whicli is 

 essentially translucid, and ought not to be confounded either with 

 stone- ware, delph-ware, pipe-clay, or even with the ordinary tender 

 English porcelain. The kilns or ovens for firing or baking hard 

 porcelain are generally cylindrical, and divided into two chambers 

 or laboratories, one placed above the other. The upper laboratory 

 is supplied with heat from the flame of the lower laboratory, and 

 serves to warm or heat the articles, which, when taken from thence, 

 are dipped into the glazing composition, and afterwards exposed 

 to the great heat in the lower laboratory, which may be properly 

 said to constitute the kiln. The fusion of the glaze or enamel, as 

 is above said, requires a very high temperature ; and it is in the 

 laboratory where this operation is carried on that the temperature 

 is raised to the highest degree. In botli these laboratories the 

 articles must be inclosed in fire-clay vessels or seggars, which 

 should he carefully closed, in order to prevent the admission of 

 deleterious matters. The necessary amount of flame and heat may 

 be obtained by increasing the number of fire-grates and openings 

 for the flame : thus a kiln or oven, six yards in diameter, which, 

 when heated with wood, requires six openings, must have ten when 

 pit-coal is employed. A kiln or oven, five yards in diameter, ^^•ould 

 require only five fire-grates for wood, but must be furnished with 

 eight for coal. A kiln or oven, four yards in diameter, heated by 

 wood, would require four fire-grates and apertures for wood, but 

 must have six for coal. In order to make the flame sufficiently 

 long and abundant for the requirements of the manufacture, the 

 combustion ought to be supplied with a double draft, or additional 

 currents of air. Thus, besides the supply furnished between the 

 fire-bars from the surrounding atmosphere in the workshop, air 

 obtained from outside is conducted by horizontal channels to the 

 fire : that is to say, besides the ordinary supply of air, an additional 

 quantity, obtained from the external atmosphere, is made to act 

 with energy on the fires in the grates. By this means, the kiln is 

 supplied with a very large and superabundant supply of air, which 

 furnishes the fuel with a much greater quantity of gas to decom- 

 pose. 



The engravings represent a kiln or oven, constructed according to 

 the present improvements ; and it should be observed, that it is 

 always easy to obtain the necessary quantity of air, by taking it 

 from the atmosphere of the workshop, either by having an aperture 

 or grating at the end of the ash-pit, or by making openings below 

 the fire-bars in the two side walls of the furnace. 



The improved system of firing or baking may be applied to all 

 kilns, whatever may be their form or dimensions ; and, by means 

 of a double roof in the upper laboratory, hard and tender porcelain 



may he fired in the same kiln simultaneously : that is to say, hard 

 porcelain may be baked or fired in the lower laboratory, at the 

 same time tliat tender porcelain or common earthenware is being 

 fired in the upper laboratory. In manufactories where at present 

 the baking of biscuit-ware and glazed ware is carried on in separate 

 kilns, it will be evident that these kilns may, by the application of 

 a double roof, be more advantageously employed in tlie following 

 manner: — In the biscuit kiln, heretofore employed, delph, or 

 earthenware, or unglazed tender porcelain, may be operated upon 

 in the lower laboratory, while hard porcelain may be dried and 

 heated in the upper laboratory; and in the other'kiln, formerly 

 used for glazing, the hard porcelain should, on the contrary, be 

 placed in the lower laboratory, to be baked or fired ; and glazed 

 delpb, or eartlienware, or tender porcelain, may be operated upon 

 in the upper laboratory, — the heat in which vvill be found sufficient 

 for this kind of ware. 



The kilns being furnished with the required quantity of fire- 

 places, the combustion must he kept up, by supplying an excess or 

 superabundance of air, obtained either from the external atmo- 

 s))here or from the workshop, and supplied in some convenient and 

 suitable manner, depending of course upon the situation of the 

 kilns, their peculiar construction, and other circumstances. The 

 tire should he gradually supplied with fuel, at first at long inter- 

 vals, then at short intervals. The state of the fire-place should be 

 looked to carefully, for it is the rapidity of the combustion of the 

 coal which indicates the quantity of fuel that is required, and the 

 moment when the charges are to he thrown on quickly. The fire- 

 places must be well watched, for the purpose of levelling the fuel, 

 so that the fire-bars may be suitably and evenly covered, and that 

 air to support combustion may always find a proper passage. It is 

 also necessary to rake the fire frequently, in order to clear out the 

 cinders, and to prevent the fire-bars from getting foul, and to re- 

 move clinkers therefrom, wliich would otherwise stop or diminish 

 the combustion. Holes through the mass of fuel should never he 

 allowed to exist, and the flame should always he well watched ; 

 and the baking or firing operation always be carried on with a long 

 flame. All these precautions are necessary, in order to obtain very 

 pure and white porcelain, as the defects of the firing operation 

 arise most frequently from the vvant of a proper flame. 



Fig. 1 represents a transverse vertical section, taken through 

 the centre of a kiln of the improved construction ; and fig. 2 is a 



Fig. 1.— Section. Fig. 2.— Plan 



horizontal section or plan of the same, a is the outer chimney or 

 flue of the upper second laboratory; b is an upper chamber, which 

 may he used for drying or heating ; p is a roof (shown by dotted 

 lines), which will be required if it is intended to hake or fire both 

 tender and hard porcelain in the same kiln ; d is the flue of the 

 lower chamber or laboratory ; e e are passages or openings, of wh ich 

 there are the same number as there are fire-places in each kiln ; 

 these passages should be placed between the fire-places, and open 

 a communication from the lower to the upper laboratory, //is 

 the lower laboratory, where the principal firing or baking operation 

 is carried on ; g g g., are the fire-places ; and h h h, openings, to 

 allow the flame to pass therefrom into the interior of the kiln, i i, 

 are the fire-bars; j j, the fire-doors; fr, the ash-pit; and //, pas- 

 sages communicating with the ash-pit from the external atmo- 



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