The Mirror of Literature, Amusement, and Instruction. Volume 19, No. 550, June 2, 1832

SPIRIT OF DISCOVERY

POTTERY. ¹¹

(Concluded from page 326.)

Wedgewood's Staffordshire Ware

Lastly is the manufacture of those species of glazed pottery known by the general name of Staffordshire ware. The date of this ware is about sixty years ago, and it unquestionably originated with the late Mr. Wedgewood. It not only originated with him, but was carried by his knowledge, his skill, and his perseverance, to a degree of excellence which, in several points, has never been surpassed, and in some has never been equalled.

He perceived that the defects of the delft ware, at that time the only species of pottery employed for common domestic purposes, were the softness and looseness of texture of its body, which obliged the potter to make it thick and clumsy and heavy, in order to ensure to it a moderate durability; and that its porousness, as well as its dirty grey colour, required a thick coating of white enamel, which added still farther to its bulk and weight, and which, consisting for the most part of lead and arsenic, was hardly safe for culinary use.

He began, therefore, by inventing a body for earthenware, which at the same time should be white, and capable of enduring a very high degree of heat without fusion, well knowing that the hardness of the ware depended on the high firing to which it has been subjected. For this purpose, rejecting the common clays of his neighbourhood, he sent as far as Dorsetshire and Devonshire for the whiter and purer pipe-clays of those counties. For the siliceous ingredient of his composition he made choice of chalk-flints, calcined and ground to powder.

It might be supposed that white sand would have answered his purpose equally well, and have been cheaper; but, being determined to give the body of his ware as great a degree of compactness as possible, it was necessary that the materials should be reduced to the state almost of an impalpable powder; and calcined flints are much more easily brought to this state by grinding than sand would be. The perfect and equable mixture of these two ingredients being a point of great importance, he did not choose to trust to the ordinary mode of treading them together when moist, but having ground them between stones separately with water to the consistence of cream, he mixed them together in this state by measure, and then, evaporating the superfluous water by boiling in large cisterns, he obtained a composition of the most perfect uniformity in every part. By the combination of these ingredients, in different proportions, and exposed to different degrees of heat, he obtained all the variety of texture required, from the bibulous ware employed for glazed articles, such as common plates and dishes, to the compact ware not requiring glazing, of which he made mortars and other similar articles. The almost infusible nature of the body allowed him also to employ a thinner and less fusible glaze, that is, one in which no more lead entered than in common flint glass, and therefore incapable of being affected by any articles of food contained or prepared in such vessels. With these materials, either in their natural white or variously coloured—black by manganese, blue by cobalt, brown and buff by iron—he produced imitations of the Etruscan vases, and of various other works of ancient art, such as the world had never before seen—such as no subsequent artist has ever attempted to rival. His copies of the Portland vase are miracles of skill; and the other specimens of similar works may give some idea of the many beautiful works that were produced in his manufactory. In table ware, for many years he led the way almost without a rival; but the immense demand occasioned by the successive improvements of this article, which first put down the use of delft, and then of pewter, gave ample room and encouragement to men of capital and skill to enter the field of profit and competition. Much good has hence resulted; many subordinate improvements have been effected and are almost daily making; and a new variety of ware, called ironstone, has been invented, and so rapidly and judiciously improved, that, in appearance and in many of its intrinsic properties, it bears a close resemblance to the older and coarser porcelains of China itself.

I shall conclude by a summary account of the manufacture of the best table ware; for a considerable part of which I am indebted to notes taken by Captain Bagnold, when visiting a pottery, inferior, perhaps, to none in the country.

The materials of the Staffordshire ware are calcined flints and clay. The flints are burnt in kilns, and then, while hot, quenched in water, by which they are cracked through their whole substance. After being quenched they are ground in mills with water. The mill is a hollow cylinder of wood bound with hoops, and having a bottom of blocks of chert, a hard, tough, siliceous stone: the mill-shaft is perpendicular, and has two horizontal arms passing through it cross-wise. Between these arms are laid loose blocks of chert, which are moved round on the bed-stone as the arms revolve, and thus grind the flint with water to the consistence of cream.

The clay, from Dorsetshire and Devonshire, is mixed with water, and in this state is passed through fine sieves to separate the grosser particles. The flint and clay are now mixed by measure, and the mud or cream is passed through a sieve in order to render the mixture more complete.

In this state it is called slip, and is now evaporated to a proper consistence in long brick troughs. It is then tempered in the pug-mill, which is an iron cylinder placed perpendicularly, in which an arbor or shaft revolves, having several knives projecting from it, the edges of which are somewhat depressed. By the revolution of these the clay is cut or kneaded, and finally is forced by their action through a hole in the bottom of the cylinder, and is now ready for use. Cups, pots, basins, and other round articles, are turned rough on the horizontal potter's wheel; and, when half dried, are again turned in a lathe. They are then fully dried in a stove, and the remaining roughnesses are afterwards removed by friction with coarse paper. Articles that are not round, and the round ones that have embossed designs on their surface, are made of thin sheets of clay rolled out like dough, and then pressed into moulds of plaster of Paris; the moulds being previously dried, absorb the superficial moisture of the clay, and thus allow it to part from them without injury. The two or three separate pieces composing the article are then united by means of fluid slip. Spouts and handles of jugs and tea-pots are made and united with the body of the vessel in the same way. Small handles, beadings, mouldings, &c. are formed by means of an iron cylinder, having its bottom perforated so as to mould the clay, as it passes through, into the required figure. A piston is inserted into the top of the cylinder, and caused to descend slowly by means of a screw, in consequence of which the clay is continually passing out through the perforation, and is cut off in lengths.

Plates are beaten or rolled out of a lump of clay, and are then laid on a mould turned to the shape of the upper surface of the plate. A rotatory motion is given to the mould, and an earthenware tool representing a section of the plate is pressed upon it; thus the plate is made smooth, has a uniform thickness given to it, and it takes a perfect cast of the mould. Cups, saucers, and basins, when rough-turned, are dried on the block to prevent them from warping.

The ware being thoroughly dried, is packed into saggars and burnt in the furnace to biscuit. Patterns for flat, or nearly flat surfaces, are put on by printing the pattern from a copper-plate with an ink composed of oxide of cobalt, oxide of iron, or other colouring matter, mixed with oil. The impression is taken on soft paper, and is applied to the surface of the biscuit, and slightly rubbed to make the print adhere: the biscuit is then soaked in water till the paper may be stripped off, leaving the print or pattern behind¹². The ware is then dipped in the glaze, which is a mixture of flint slip and white lead, and the bibulous quality of the biscuit causes a sufficient quantity to adhere: the piece is then dried and again passed into the furnace, which brings out the colours of the pattern, and at the same time vitrifies the glaze.

The finest patterns are applied after the glazing has been completed, by taking the impressions from the copperplate on a flexible strap covered with a strong gelatinous mixture of glue and treacle. This strap is then pressed on the ware, and gives the impression in glue, the colouring powder is then dusted over it, and a sufficient portion adheres to the damp parts to give the pattern, after having been again in the furnace. The more elaborate patterns on earthenware, and all those on porcelain, are finished by penciling in.