fuel in England has led to the wasteful and unscientific application of it in many of our manufactories, and the slip-kiln is one out of numerous examples. In countries where fuel is scarce, the slip is deprived of its superfluous water by other means. In the potteries of Röstrand near Stockholm the slip is placed in large square boxes, and exposed to the air with a southern aspect, by which means a large quantity of water is got rid of by the natural process of evaporation. The boxes are furnished with covers, which are lowered in rainy weather. When a certain quantity of water has been got rid of in this way, the paste is put into the hollow cavities of thick plaster moulds, which absorb sufficient water to bring the paste to the proper consistency for working. It is necessary to keep the slip in a state of agitation in the moulds, or the resulting paste will be denser where it comes in contact with the plaster than in the other parts. This plan can only be practised on a small scale; but we are now about to notice two methods, both of which deserve the serious attention of manufacturers. The first consists in enclosing the slip in sacks of strong and closely woven texture, and then subjecting it to a considerable pressure, which may be economically supplied by means of a long lever loaded at the end of the long arm, and a number of sacks being placed between two boards near the end of the shorter arm, the pressure is thus maintained as long as it is required. A press of this kind will prepare about 1,300 lb. of porcelain paste in 3 hours. A screw press worked and attended by 2 men, will prepare in a day of 12 hours from 1,350 to 1,575 lbs. of porcelain paste.

for use

It will be seen that this method is a species of filtration accelerated by mechanical pressure. A more refined and successful plan is to filter with the aid of atmospheric pressure, for which purpose the filter is placed above the vessels AA, Fig. 1701, from which the air can be removed by connecting them at bottom with a tube about 36 feet long, terminating at its lower extremity in a reservoir of water c. If one of these vessels be full of water, and be made to communicate with the reservoir by means of the long pipe, a vertical column of water from 40 to 50 feet in height will thus be formed; but as the atmospheric pressure is only equivalent to a column of about 34 feet high, [see AIR,] it is evident that the upper part of the column will sink down to that height, or in other words, the vessel A will discharge its contents into the reservoir c by means of the pipe, and thus form a vacuum above. The slip is contained in the filtering vessels, FF, above, in the centre of each of which is an opening communicating by pipes with the vessels AA. This opening is covered with an iron grating g, and a bed of pebbles, p, is made to cover the rest of the conical part of the filter. The grating and the pebbles are covered with a cloth of thick spongy felt, pervious to water but not to the solid particles of the slip, firmly secured at the edge of the filter, and above this is another cloth of hemp for receiving the slip. On opening the stop-cocks cc, so as to connect one of

paration of porcelain than of pottery paste. For the latter the form of apparatus shown in Fig. 1702 may be used. In this the vacuum is produced by injecting steam into cylinders c, placed below the filtering bed. The vessel containing the filter is of cast-iron; the filtering cloth is shown at c, resting on its bed of pebbles P: g is the grating as before.

In the English process, when the slip has been reduced to the proper texture in the kiln, it is removed to another part of the slip-house, where the process of wedging goes on. This consists in cutting up the mass from the slip-kiln into wedges by means of a spade, and dashing them against each other to get rid of vesicles and air-bubbles, which would otherwise form blisters in the ware. This wedging should be carried on at intervals during several months, to secure a fine grain and freedom from flaws. In China, we are told, a store of clay is prepared 14 or 20 years in advance, and sometimes a potter will prepare suffi

Fig. 1706.

the thrower's foot by means of a forked lever, so that he can shift it at pleasure to a wide or to a narrow part of the cone.

As soon as one vessel is formed, and cut off at the base with a fine brass wire, the baller supplies another ball of clay, and the new-made vessel, (now said to be in its green state,) which he lifts off the wheel, is placed on a board, and when a sufficient number are collected, he carries the whole into the open air, or into a warm room, where they part with their moisture sufficiently to allow of the next process which is turning.

The turning of earthenware in the Staffordshire

WARE BOTTLE.

up, is performed by placing one hand in the vessel No. 3 and the other on the outside, and pressing the clay between the knuckles of the two hands, at the same time raising the arms, the thick sides of No. 3 are thinned out into No. 4, the board or wheel of course being kept revolving all the time at various rates of speed as experience suggests. The next process is to make the sides truly cylindrical, which is done by the hand inside and a flat rib outside opposed to each other. A flat surface somewhat corresponding to the rib is formed by the hand inside by stretching out the index finger straight against the thumb as shown in the figure. The wide parts of No. 5 being carefully finished, the neck is gradually contracted and the top finished as in No. 6. The bottle is then cut off by passing a wire between it and the board, but before removing it from the board a list stopple is put into the mouth for the purpose of confining the air. If it were not for this simple but not very obvious precaution the large heavy mass of soft hollow clay would collapse in being removed, but by stopping the mouth the enclosed air acts as a sort of cushion or elastic support to the mass. When the bottle has become sufficiently consolidated by drying it undergoes the operation of turning (see Fig. 1706,) as will presently be noticed, the handle is glued on by means of slip, and it is ready for firing.

In large potteries, where a number of potters' wheels or lathes are in use, they are turned by means

That

or metal, and it is a curious sight to watch a rude clay cup or bowl spinning round in the turner's lathe, with long and broad shavings flying off from it, under the operation of the cutting tools. the turner may stand quite steady at his work, motion is given to the lathe by an assistant treader. This is usually a female; and while employing her right foot at the treadle, she also attends to the green vessels on the board, moistening their upper edges, and clearing away whatever interferes with the turning. A clay ring, scarcely moist, is kept on the chuck, the vessel is put on it with the upper edge (already moistened) turned downwards, and pressed into the clay ring. The surplus clay, left by the thrower, is then rapidly removed by the tool, and the vessel brought to the required thickness. When this has been completed, and any desired fanciful indentations and cuttings have been made, then a retrograde motion is given to the spindle, during which the upper surface of the vessel is smoothed and solidified by the pressure of a broad tool, and the vessel is then cut loose, and delivered to the handler, or it is dried for the biscuit oven. Clay for handles, spouts, &c. is first formed into pipes at a small press, which forces the clay through a metal tube of the required size and form. The clay pipes, thus formed, are cut up into lengths, and shaped with the hand. They are attached to the articles by means of slip, which unites them quickly and perfectly. Superfluous clay is scraped off with a knife, and the vessel cleaned with a damp

sponge, to give it a uniform appearance. Plaster-ofParis, or steel moulds, are used where figures and foliage are required, and are attached as before. In some cases flowers and leaves are formed by hand, with considerable dexterity and attention to botanical character. The Editor has witnessed the skill exhibited in this respect by the artists employed in the celebrated porcelain works at Meissen, near Dresden, where a botanist of talent is employed to superintend the operations.

When articles have to be executed on a large scale, the method is the same in principle as that just alluded to of forming ornaments in moulds, and is called pressing. Plaster moulds of every variety of size and pattern are employed in great numbers, for all plates and dishes are thus manufactured, and a complete set of patterns is required for every new pattern, and for every size of the same pattern. Moulds for plates and other shallow articles consist of only one piece, and are formed by taking the impression of the inside of the article, or the upper surface of the model in plaster. Plates, dishes, saucers, cups, and hand basins are now made by the process of flat-ware pressing, an operation which is conducted as follows:-a plate being taken as an example. The plate-maker stands at a bench before a whirling table similar to the thrower's, but moved by a horizontal pulley or jigger turned by a boy. On his left hand is a batting block of wet plaster and a mass of well beaten clay. Near him is the stove-room in which moulds are ranged on shelves to dry. The platemaker first cuts his clay into lengths with a wire, and tears off a piece which he batts out thin upon his block by a stroke or two of his batter, which is a plaster mallet, and he polishes the surface of the batted clay by pressing the side of a smooth knife against it. The boy then places a mould on the whirler, and stations himself at the handle of the jigger: the man places the clay on the mould, which is then set whirling, and he presses it down close with his hand. A profile or earthenware tool, which gives the form to the bottom of the plate, is next pressed upon it as it revolves. Where great precision is required, the profile is mounted in a carrier c, Fig. 1707, which can be adjusted by screws upon

Fig. 1707.

the arm I of the frame FF, and fixed to the proper height by the screw R. The arm I descends in a groove g, to the exact depth required for the thickness of the plate. When the proper shape is given the motion is stopped, and the boy catching up the mould with the plate upon it runs with it to the hot room, places it on a shelf to dry, and returns with an

empty mould which has been drying. In the mean time the man has batted out another piece of clay for another plate. In about two hours, the plates become sufficiently dry to be removed from the moulds, but the moulds themselves having absorbed much moisture from the plates, are left to dry before they can be again used. One workman, with the assistance of two boys, can make from 60 to 70 dozen of ordinary plates in a day of 10 hours, using the same moulds about five or six times in the period.

The whirling table having a circular motion, is of course only adapted to articles with a circular outline. At the Royal porcelain works at Meissen we saw a whirling table with an elliptical motion, adapted to dishes and other articles. For articles of less regular figure, the whirling table is not moved by a wheel and strap, but is simply supported at the end of the vertical rod, and left free to turn on receiving a gentle impulse from the moulder. Where the surface of a large article has to be covered, the clay is rolled out upon a moistened sheepskin, the rolling-pin being supported by two guide rules. The clay is lifted by means of the skin, placed upon the mould, pressed, smoothed, and adjusted, and finished with a wet sponge, and wet leather. The edges are then trimmed, and the maker's name or other mark is stamped upon the back.

The above simple form of pressing is not applicable to deeper vessels, which are made by what is called hollow-ware pressing or squeezing. The mould in this case is made in several parts, accurately fitting together, as shown in Fig. 1708, which represents a mould for a

foot-pan. The base of the mould has 4 projections, which fit into cavities of the two halves for the upright portion. One of these uprights is shown with the pan in it in the act of being detached. In moulding such an article, the clay is well kneaded, batted out, and spread over the bottom, which is placed on a whirler or flat board mounted on a vertical axis, so as to turn round easily: the two halves are each lined with clay, which is well worked into the grooves and made to project a little at the edges. Each half is then placed upon the base piece, and secured by passing a string round the outside of the mould. The joints are then well worked with the wet finger, and fresh clay added, and slip applied so as to make the seams adhere perfectly. The mould is then put aside, and another filled in like manner. Handles for large vessels are prepared in plaster dies or moulds. For lugs. or solid handles, the clay is well rammed into

Fig. 1711.

Fig. 1712.

and generally of some rich or deep colour. This completely covers the surface, and hides the pattern, which is to be revealed by an after process. In 24 hours the slip becomes tolerably hard: the tile is then placed on a small whirler, and the pattern and the ground are brought out by scraping away the superfluous clay, Fig. 1712, and leaving it only in the depression caused by the pattern mould. The whole is finished with a knife, and defects corrected: the edges are squared, and their sharpness rounded off with sand-paper. The tiles are kept for a week in a warm room called the green-house, whence they are subsequently conveyed to a hot-house, where strong heat completes the drying. They are then arranged in seggars, and fired as in baking pottery and porcelain, only about double the time is required. The oven is left to cool for six days, and the tiles are then drawn in their finished state. These tiles contract in firing to the extent of th or th in every inch. The dry tiles contract about from th to th. The above process is nearly the same as that employed in the middle ages, in making pavements for churches both in France and England, and also for the beautiful pottery called Henry II.'s ware, prevalent in the 16th century. These processes are being largely adopted in Prussia. In the architectural court of the Great Exhibition were specimens of tiles manufactured on the dry method by Mr. Minton, in imitation of terracotta stone. The introduction of such ornamental works instead of carved stone, is a great point as it respects economy. The manufacture of terra-cotta, or baked clay resembling stone, is likely to become an important branch of industry in England, if the material can be made to resist the climate, and brave the effects of frost. The clay requires to be fired to the point at which the cohesion of the particles exceeds the expansive power of water when frozen. When the clay used cannot itself be made to acquire that power, some calcareous clay, or some vitreous material is added, in due proportion. In Vienna some of the finest buildings are wholly ornamented in terracotta, and there is no doubt of its adoption here, if it should be found sufficiently durable.

SECTION VII.-FIRING.

The vessels and other articles produced by throwing, pressing, and other processes, described in the

The temperature at which ceramic wares are fired has a great influence on their character and texture. The usual effect of firing is to convert the article into a hard sonorous biscuit, more or less porous, and requiring the application of glaze and a second firing in order to remove the porosity and give a durable smooth surface not very liable to tarnish. In the case of porcelain, the temperature of the first firing is sufficient for incipient vitrification, so that, as far as use is concerned, the article is complete at one firing; the second firing being for the purpose of fixing enamel ornaments, &c. The firing of ceramic wares is a costly process, on account of the great expenditure of time and fuel. It was, therefore, a great improvement when Wedgwood introduced a ware so compounded that partial vitrification took place at the first firing, thus rendering a second unnecessary. The Lambeth potters, also, by the ingenious artifice already noticed (SEC. II.) of throwing salt into the kiln at a certain stage of the firing, manage to fire and glaze certain coarse wares at one process.

The arrangement of the kiln for firing ceramic wares varies with the nature of the wares themselves and the kind of fuel employed. Fig. 1713 represents a section of the pottery kiln. It is a massive cylinder