MEDIEVAL TILE MAKING
Tile making was associated with monasteries and palaces, the large buildings of their time. The potters travelled around the country using local clays and firing them on site. The tiles were made by hand, flattening the clay and cutting pieces into shape. The only mechanical aid was a wooden mould carved in relief, which indented a pattern on the clay slab. The slab was dried and the impression filed with white pipe clay, which after further drying was shaved flat. A glaze of lead ore was sprinkled onto the surface and the tiles were fired. These 'encaustic' or inlaid tiles were made from the 12th to 16th centuries, the skill dying with the dissolution of the monasteries, and was not revived until the middle of the 19th century.
On the continent in the medieval period, wall tiles were made with a white tin glaze and painted in bright enamel colours. By the end of the 16th century the Dutch potters based at Delf, were exporting their blue and white tiles throughout Europe and the New World. The craftsmen also travelled. Dutch potters began manufacturing in Lambeth in about 1647, and from there spread to Liverpool and Bristol. The tiles were made by hand with the aid of a frame to produce an even size. The tiles were either painted free-hand, or designs were taken from engravings by 'pouncing'. The outline of a picture was pricked out on a piece of paper and powdered pumice, or pounce, was rubbed through the holes onto the tile. This outline was then painted, and other tints were added.
In 1756 two Liverpool printers, John Sadler and Guy Green, signed an affidavit that they had printed 1200 tiles in six hours. This new method of decorating had great impact not only on the tile industry but the ceramics industry as a whole. A copper plate was engraved with a design, this would be covered in colour, the excess removed leaving the colour only in the engraved parts. A tissue paper was pressed onto the plate, removed, and the colour transferred to the tile. This method was quicker, and therefore cheaper than hand painting. Sadler and Green did not make tiles, they were supplied with blanks by manufacturers. In 1761 an association started with Josiah Wedgwood to print his creamware. This led to an expansion of business as this body was more durable and less likely to chip than delftware tiles, the production of which virtually ceased by 1790.
ENCAUSTIC TILE REVIVAL
Archaeological excavations of medieval sites aroused much interest in encaustic tile making. Herbert Minton began experimenting in 1828, and in 1830 bought a half share in Samuel Wright's patent for the production of encaustic tiles. It was several more years before their results were reliable, and a catalogue was issued in 1835 containing designs based on medieval originals. Very soon he was receiving commissions from churches to lay encaustic tile pavements, and success was guaranteed when he found the patronage of Queen Victoria and Prince Albert making a pavement for Osbourne House. The fashion for encaustic tiles spread with the Gothic Revival lead by Augustus Pugin who was a friend of Herbert Minton. Encaustic tile making was the greatest stimulus to the development of the Staffordshire tile making industry in the nineteenth century. The district was a natural centre as clay and coal were available, and a skilled workforce to call on because of the established pottery industry.
MAKING ENCAUSTIC TILES - PLASTIC CLAY
The mixture for the tile body might contain red clay or ball clay, china clay and flint. Chemicals were added to produce the different colours. Water was added to form a slip (liquid clay) which was sieved. The clay was dried on plaster bats, which absorbed the water to bring it to a plastic state. A pug mill then tempered the clay (formed a compact mass with no air bubbles.) The tile was formed in a metal frame, the relief pattern that formed the indentation in the bottom. The clay was added in a sandwich fashion: firstly a quarter inch of fine clay; a thick coarse clay layer; then a quarter inch of fine clay. This method prevented warping, and gave a fine clay surface while the body was robust. A plate was placed over the frame and the layers pressed together. The tile was allowed to dry, then slip was poured onto the surface filling the indented pattern. After three days, drying the surface was scraped to reveal the design and after further drying they were fired. This process was manual except for the few machines that prepared the clay.
MAKING WALL TILES
In 1840 Richard Prosser patented a process for making clay buttons from dust clay. Herbert Minton was quick to realise that this process could be converted to make ceramic tiles, and he bought a share in the patent. The wall tiles were different from the encaustic in that they were lighter and had a larger proportion of calcined flint to produce a white body and usually a surface glaze decoration. The clay was cleaned and dried in heated troughs. It was important to obtain the right water content, as the clay felt dry - hence 'dust clay'. After leaving the drying beds, the clay was ground to a fine dust that had natural cohesion when under pressure, and could be handled without further drying. If a tile had a surface pattern a die was placed into the tile press. The presser wiped the plates of his press with a greasy rag, filled the mould with dust clay and scraped the surface level. He lowered the press by turning a large horizontal wheel at the top, this exerted enormous pressure on the face of the tile and thus compacted it. The tile was forced out of the press by a foot pedal. This method changed little throughout the 19th century except for the invention of the steam driven press first used by Maws in 1873.
MAKING ENCAUSTIC TILES - DUST CLAY
In 1863 William Boulton patented a method of making encaustic tiles using dust clay. The patterned part of the tile was formed using one or more copper plates which were perforated to the required design. Guide pegs located the plate on the bed of the press and the hollows in the mould were filled with dust clay. A die whose relief pattern corresponded to that of the plate was used to compress the clay, a ram coming down in such a way that the plate was removed as it returned. The frame was filled with more clay of a different colour that would form the body. As this was compacted, the inlaid section was bedded into the face of the tile. This method increase speed of production and thus a cheaper tile was available to a wider market. The dust pressed process never ousted the plastic clay method, and the two ran side by side.
19th century tiles were fired in bottle ovens. The tiles were stacked in saggars which protected then from smoke, and helped give an even distribution of heat within the stack. Opening around the base of the kiln gave access to several fires that fed into a central flue. The biscuit (first) firing had the highest temperature at 1060 C that fixed the tiles for size and shape. After glazing the tiles were glost fired at about 1020 1240 C. On glaze decoration was fired at 750 C, just before the glaze began to melt.
Victorian potters had a large cheap labour force. Consequently, many experiments in tile decoration were carried out, much of the work being done by hand. Decorated wall tiles came into general use in the 1870s, the basic methods being as follows:
ENCAUSTIC: A clay pattern was embedded into the body of the tile, the two sections fusing during firing.
PLAIN GLAZES: White lead, flint, china stone and china clay were ground to form a glaze. Ground metal oxides could be added to give different colours. A clear glaze brought out the natural body colour and might be applied over any coloured decoration.
HANDPAINTING: The artist painted freely onto a plain surface tile. A design could also be copied from an original sketch by 'pouncing'. Alternatively a tile could be transfer printed and coloured by hand.
SGRAFFITO: An early form of decoration, the tile body is covered with coats of slip that is scratched off to produce the design.
TUBE LINING: Slip is trailed onto the surface of the tile to make raised lines separating the areas where different colour is wanted. Coloured glazes were then applied. This technique was used for Art Nouveau tiles.
TRANSFER PRINTING: This was the most common method of decorating Victorian wall tiles. The design was printed onto tissue paper, which was placed colour side down onto the tile. The colour was transferred by rubbing it down, and the paper removed.
The skills involved in decorating were greater than those for making the tile body as the chemical changes of glazes and colours was uncertain during firing.
TILE MAKING IN THE 20TH CENTURY
The basic dust pressed process had remained but a flow line production has been achieved by mechanisation. The slip is dried in a special spray dryer to produce 'dust particles', and the dust pressed tiles are automatically processed on a belt until they are ready for packing. The firing is in continuous tunnel kilns fired by gas or electricity.