627 



Soon after the fire is lighted, tho flame, which communicates laterally from one 

 furnace to another, envelopes the muffle on all sides, and thence rises up the chimney. 

 A patent was obtained by Mr. W. Ridgway for the following construction of oven, 

 in which tho flames from the fireplaces are conveyed by parallel flues, both hori- 

 zontal and vertical, so as to reverberate the whole of the flame and heat upon 

 the goods after its ascension from tho flues. His oven is built square instead 

 of round, a fire-proof partition-wall being built across the middle of it, dividing 

 it into two chambers, which are covered in by two parallel arches. The fire- 

 places are built in the two sides of the oven opposite to the partition-wall : from 

 which fireplaces narrow flues rise in the inner face of the wall, and distribute the 

 flame in a sheet equally over the whole of its surface. Tho other portion of the heat 

 is conveyed by many parallel or diverging horizontal flues, under and across the floor 

 or hearth of the oven, to the middle or partition- wall ; over the surface of which the 

 flame which ascends from the numerous flues in immediate contact with the wall is 

 equally distributed. This sheet of ascending flame strikes the shoulder of the arch, 

 and is reverberated from the saggers beneath, till it meets the flame reverberated from 

 the opposite side of the arch, and both escape at the top of the oven. The same con- 

 struction is also applied to the opposite chamber. In Jigs. 1661 and 1662, arepresents 

 the square walls or body of the oven ; b, the partition-wall ; c, the fireplaces or 

 furnaces, with their iron boilers ; d, the mouths of the furnaces for introducing the 

 fuel ; /, the ash-pits ; g, the horizontal flues under the hearth of the oven ; h, the 

 vertical flues ; , the vents in the top of the arches ; and k, the entrances to the 

 chambers of the ovens, 



1661 



1662 



Before this article is concluded it is necessary that we should notice the attempts 

 which have been made, with various degrees of success, to employ porcelain as 

 a means for multiplying the productions of high art in a cheap form. Under the 

 various terms of Statuary Porcelain, Parian, Carrara, &c., are produced numerous 

 works of art, many of which are distinguished by their beauty. As the most direct 

 method of illustrating the process of making these figures, let us suppose tho object 

 under view to be a figure or group, and this we will assume to be 2 feet high in the 

 model. The clay, which is of the most perfect character, is mixed with flint, as in 

 the case of manufacturing the finest stoneware china, and it is used in a semi-liquid 

 state about the consistency of cream : this is poured into the moulds forming the 

 various parts of the subject (sometimes as many as fifty) : the shrinking that occurs 

 before these casts can be taken out of the mould, which is caused by the absorbent 

 nature of the plaster of which the mould is composed, is equal to a reduction of one 

 inch and a half in the height. The moulds are made of plaster of Paris, which, 

 when properly prepared, has the property of absorbing water so effectually that the 

 moisture is extracted from the clay, and the ware is enabled to leave the mould, 

 or ' deliver ' with care and rapidity. Prior to use, the plaster (gypsum) is put into 

 long troughs, having a fire running underneath them, by which means the water 

 is drawn off, and it remains in a state of soft powder : and if its own proportion 

 of water be again added to it, it will immediately set into a firm compact body, which 

 is the case when it is mixed to form the mould. These casts are then put together 

 by the ' figure-maker,' the seams (consequent upon the marks caused by the sub- 

 divisions of the moulds) are then carefully removed, and the whole worked upon to 

 restore tho cast to the same degree of finish as the original model. The work is then 

 thoroughly dried to be in a fit state for firing, as if put in the oven while damp the 

 sudden contraction consequent upon the great degree of heat instantaneously applied, 

 would be very liable to cause it to crack ; in the t>rocess it again suffers a further loss 



as2 



