CHAMBERS'S INFORMATION FOR THE PEOPLE. 



the Roman power, the art of glazing seems to 

 have been lost, or was only known in Europe to 

 the Moors, who practised it in Spain in the eighth 

 century, chiefly for the decoration of their beauti- 

 ful wall-tiles (Azulejos). They possessed the art of 

 applying metallic and iridescent glazes of great 

 beauty. When they were expelled from Spain, 

 they carried their manufacture of pottery into 

 the Balearic Isles, and for a considerable time, 

 Majorca was its chief seat ; whence the beautiful 

 painted and glazed pottery of that and subsequent 

 periods has been called Majolica, or Maiolica ; 

 the latter name is now rising in favour amongst 

 connoisseurs. From Majorca it was introduced 

 into Portugal, Italy, and France, and thence into 

 Holland. In the seventeenth century, a pottery 

 was established at Burslem, in Staffordshire at 

 which, however, only the coarsest articles of brown 

 ware were manufactured. Subsequently, the glaz- 

 ing of this ware by the vapour of salt ob- 

 tained by throwing handfuls amongst the heated 

 articles in the kiln was introduced by Mr Palmer ; 

 and in this state the manufacture continued till 

 1690, when two Dutchmen of the name of Elers 

 commenced at the same place the fabrication of 

 red unglazed porcelain, of black or Egyptian ware 

 the tint of which was produced by manganese 

 and of brown ware of a higher glaze and finish 

 than had hitherto been produced in England. 

 Some years afterwards, Mr Astbury was led by 

 accident to attempt the admixture of ground flint 

 with the finest white clay a composition which 

 yielded not only a finer and whiter, but a more 

 durable ware than had previously been manu- 

 factured. It is to Josiah Wedgwood, however, 

 that Britain is mainly indebted for the vast 

 improvements which have taken place since 

 the middle of last century in this department of 

 her manufacturing industry. It was he who 

 erected the first large factories in Staffordshire, 

 and who, from his extensive chemical and mechani- 

 cal knowledge, conjoined with correct taste, has 

 made the stoneware manufactures of this country 

 superior to those of every other. 



Under the general designation of pottery are 

 included three different kinds namely, earthen- 

 ware, stoneware, and porcelain, but it is frequently 

 applied specially to earthenware, to distinguish it 

 from the other two varieties. In this sense, it 

 means those ceramic manufactures made from 

 natural clays, or from clays with the addition of 

 sand or calcined flint ; whilst stoneware is made 

 of clay with a considerable addition of pure silica, 

 usually obtained by grinding down blocks of 

 decomposing Cornish granite, and some lime ; and 

 porcelain is a compound of kaolin or China clay, 

 or decomposed felspar, with pure silica and other 

 materials in various proportions to form the 

 various qualities. 



The best clay for pottery manufacture is obtained 

 in Dorsetshire, and another of a quality some- 

 what inferior is found in Devonshire. These 

 clays are both well suited for the potter, being 

 easily worked, standing the fire well, and becom- 

 ing very white when burned. When dug, the clay 

 should be cleansed as much as possible with the 

 hand, and freed from stones. At the factory, it is 

 cut to pieces,. and put into a cast-iron cylinder, 

 about four feet high and twenty inches in diameter. 

 An upright shaft or axis revolves in this cylinder, 

 from which knives radiate in all directions, being 



356 



so placed that the shaft with the knives attached 

 somewhat resembles a screw. In the sides of the 

 cylinder, knives are also fixed, which reach nearly 

 to the shaft, and remain inactive. When the 

 shaft moves round, the active blades cross the 

 passive, and operate like shears in cutting the 

 clay, which is by this process reduced to a fine 

 paste. The external appearance of the machine 

 much resembles the ' pugging-mill' in fig. i. 

 When well ground in this manner, the clay is 

 reduced by water to the consistence of cream, 

 and is run off through sieves of wire, lawn, and 

 silk, so that none of the grosser parts may enter 

 into the composition of the ware. This clay- 

 cream, or slip, as it is termed, is flien diluted to 

 a standard density, and set aside in cisterns, to 

 be used as required. 



The clay thus prepared possesses remarkable 

 plasticity ; it is sensitive to the slightest pressure, 

 and retains any form or impjression given to it. 

 But this high degree of plasticity brings with it 

 sundry inconveniences : thus, in the firing, the 

 articles are apt to crack, and also to become dis- 

 torted. This distortion does not arise, it is sup- 

 posed, merely from the evaporation of the water, 

 but from the tendency of the particles to assume 

 their normal condition, out of which they were 

 forced by the processes of pressing and twisting, 

 or ' throwing,' to which the clay is subjected. To 

 prevent this cracking and distortion, it is necessary 

 to add some silicious substance, incapable of con- 

 traction, to the clay. Ground flint is most com- 

 monly used for this purpose. It is prepared by 

 cleaning the flint found imbedded in chalk, sub- 

 jecting it to a red heat, and throwing it in this 

 state into water, by which it becomes compara- 

 tively soft. It. is then broken by being placed 

 under upright shafts, which move up and down in 

 a frame, and are called stampers. The broken 

 flint is next transferred to the flint-mill, which 

 consists of a strong wooden tub, built round a 

 circular bottom, composed of flat pieces of horn- 

 stone. On the top of these, similar flat stones are 

 laid, which are attached to, and driven by, strong 

 wooden arms projecting from an upright shaft in 

 the centre of the box. Into this 

 tub the flint is put, and a stream 

 of water is constantly running in, 

 which greatly facilitates the grind- 

 ing. In fig. 4, a, a represent the 

 revolving arms, and b, b the stones 

 fixed to them. When the flint is 

 reduced to about the consistence 

 of cream, it is passed through 

 sieves, in a manner similar to the clay. 



The flint and clay liquids being properly pre- 

 pared, they are next mixed together in such pro- 

 portions that the flint will be to the clay as one 

 to five or six, according to the plasticity of the 

 clay. Sometimes a little Cornish stone is also 

 added ; and the following are the proportions 

 generally adopted in one of the principal Stafford- 

 shire factories for what is designated cream 

 colour: Silex, or ground flint, 20 parts; clay, 

 loo parts ; and Cornish stone, 2 parts. This 

 mixture is put into oblong stone troughs, called 

 slip-kilns, bottomed with fire-tiles, and placed 

 above a furnace flue. Heat is then applied, and 

 the water gradually evaporated, the liquid being 

 constantly stirred during the operation. By this 

 process, the mixture is formed into a fine uniform 



Fig. 4- 



