Aerograph: A small, precise spray gun mainly used with stencils to create patterns on tiles and other materials. The nozzle can be adjusted to give a solid dense spray or a fine mist that can be used for shading.

Art Deco: An art and architecture movement of the 1920s and 1930s, noted for its bold geometric patterns and colors. The style is also sometimes referred to as ‘Moderne’.

Art Nouveau: An art and architecture movement established in the mid-1890s, noted for its use of sinuous design elements, often incorporating stylized floral or figurative motifs. It was named after l’Art Nouveau, a shop in Paris, France that first promoted the style. [Victorian Web section on Art Nouveau]

Barbotine: Using pigmented slip clays to paint a design on a tile (or other) surface. The design is painted over many times to create a raised effect on the tile surface. (See also: Pâte-sur-Pâte)

Biscuit: A tile that has been biscuit-fired, before any decoration or glaze has been applied.

Biscuit-Firing: The first firing that hardens the body ready for decoration and/or glazing.

Block Printing: A form of lithographic printing. The German engraver Aloys Senefelder (1771–1834) invented lithography in 1798. The printing surface is a smooth stone block with the printing and nonprinting areas being made grease-receptive and grease-repellent respectively. Greasy ink is then rolled over the entire area and is taken up only by the grease-receptive areas. Paper is then pressed onto the stone and the ink transfers to the paper, which is then applied to the tile front. (See also: Collins and Reynolds Patent; Transfer-printing)

Blunger: A large vat with rotating paddles used to mix clays and water to produce slip.

Body: A mixture of clays formulated for a specific purpose, i.e. color, texture or frost resistance etc.

Bottle Kiln: A traditional brick-built kiln whose shape resembles a large squat bottle.

Ceramic Colors: Pigments that are able to withstand the firing temperature of ceramics, i.e. in excess of 1000º Celsius.

Clay: A natural material (mainly alumina silicate) formed from the weathering and decomposition of rocks. It is found in most parts of the world and in many different colors due to contamination with various other materials such as iron. It is easily shaped and holds its shape well, once dried. The shape becomes permanent when the clay is fired. (See also Plastic Clay & Dust Clay)

Cloisonné: The Dutch term for Cuenca.

Cobalt Blue: A rich, deep blue ceramic color produced from compounds of the metallic element Cobalt, much used in the Far East and on Dutch and English delftwares. The main source is Zaffer, a cobalt ore found widely in the Middle East.

Collins and Reynolds Patent: A patent method of block printing onto tile surfaces that was much used by Herbert Minton who bought the rights to the patent in 1848. Minton referred to the technique as the New Press process and produced many different series of picture tiles by this method, as well as geometric and floral patterns.

Cuenca: From the Spanish meaning ‘bowl’. The term is used for tiles that have raised lines molded onto the surface to prevent different colored glazes running together in the firing. (See also Cloisonné)

Cuerda Seca: From the Spanish meaning ‘dry cord’. In its earliest form, a thin cord impregnated with a waxy substance was laid in a pattern on the surface of the tile to contain and separate different colored glazes. Later, the line was drawn or printed on the surface of the tile with a waxy substance containing manganese pigment. The resultant tiles have a distinctive sunken matt black line surrounding each color in the pattern.

Crazing: Minor ‘fracturing’ of the glaze surface due to one of a number of reasons: differing shrinkage rates of biscuit and glaze in the glost firing, absorption of moisture causing the tile body to swell, or slight flexing of the tile after installation. The presence of dissolved salts in moisture absorbed from the wall or floor on which the tiles are fixed can, in extreme cases, cause the glaze to flake off completely.

Crackle Glaze/Crackelure: The deliberate use of additives in the glaze designed to re-create the effects of crazing. Often used to create a false impression of age.

Delftware: A term applied to tin-glazed earthenwares, mainly from the Netherlands and Great Britain, generally decorated with cobalt blue or manganese purple pigments. Named after the Dutch town of Delft, a major centre for its production from the seventeenth century to the present day.

Dust Clay: Clay that has been dried to approx 8% moisture content, creating a damp powder that can be easily formed by dust-pressing. Drying was originally done in a filter-press where the wet clay was placed in large filter bags and squeezed dry, the water escaping through the bag material. In more recent times, the clay is spray-dried by pumping through a nozzle past a stream of very hot air, causing the moisture to evaporate rapidly.

Dust-Pressing: The technique of manufacturing clay tiles from dust-clay. The damp powdered clay is placed into a screw press and compacted under high pressure to create a tile body that is ready for decoration and can be fired without further drying. This method is the basis of all modern mass-produced tiles. (See Prosser’s Patent)

Earthenware: Clay bodies that fire at a comparatively low temperature (700º to 1200º C, 1300º to 2200ºF), producing a semi-porous material used for making tiles, bricks and utilitarian pottery.

Emaux Ombrants: From the French meaning “shadowy enamels”. This technique involves intaglio molding the surface of a tile or other object and then flooding it with a soft glaze that flows freely in the firing. The glaze runs off the high points and into the lower recesses of the molding to create a tonal variation. This was the technique used by Sherwin and Cotton and others to create so-called “photographic tiles”. These often utilized a dark brown or black glaze to enhance the effect of a photograph.

Enamels: Low temperature colors applied over-glaze in a muffle kiln. Not as durable as ceramic colors, but available in a much wider variety of shades and effects.

Encaustic Tiles: Tiles with an inlaid pattern created from different colored or stained clays. A die is used to form an intaglio pattern in the front of a plastic clay tile and the resulting depressions are filled with a contrasting color of slip clay. Encaustic tiles were also produced by dust-pressing using a complex system of pierced metal plates or lattices placed in the bottom of the screw press to separate different colored dust-clays.

Engobe: A thin layer of slip applied to a tile to provide a surface for decoration (sgraffito or sgraffiato) or to change the top color of the tile body.

Extruded: Tiles that have been formed by squeezing clay through a shaped nozzle under high pressure. The process produces a continuous strip, either flat or relief molded, which is then cut into lengths to form the tiles.

Faïence (I): A tin-glazed earthenware painted with a wide palette of ceramic colors on a white tin-glaze background. Named after the town of Faenza in Italy, a major fifteenth- and sixteenth century centre for the production of such wares. See also Maiolica.

Faïence (II): In the U.K., the term is often applied to large-scale glazed terra cotta or frost-proof tiles for architectural use.

Fireclay: A coarse but durable clay that is used for making saggers, the ceramic boxes in which pottery is fired, protecting it from direct contact with the flames. Fireclay is also used to make heavy-duty tiles, some forms of terra cotta and grog.

Firing: The process of baking ceramics in a kiln to create a hard, usable material. (See also: Biscuit-Firing; Glost-Firing)

Glaze: A thin glass-like film fired onto the surface of ceramics to create a smooth, decorative and protective surface. It can be transparent or opaque, glossy or matt. It seals the surface making it less prone to dirt and moisture. (See also: Tin-Glaze; Lead-Glaze; Over-Glaze; Under-Glaze; In-Glaze)

Glaze-Trailing: Applying glaze with a broad nozzle (originally a cow-horn or similar), to create a wide line of colored glaze.

Glazing: The process of applying a glaze. Glazes can be applied by dipping, brushing or spraying.

Glost-Firing: The second and/or subsequent firing required to fuse the glaze to a biscuit tile.

Grog: Coarsely ground pre-fired ceramic material, usually fireclay, which is mixed with natural clays to improve workability and strength.

Grout: A cementitious material forced into the joints between tiles after fixing. It keeps moisture and dirt out of the joints and enhances the beauty of the finished product.

Incised: A pattern formed by cutting into the surface of the tile with a sharp point or knife before firing.

In-Glaze: A technique of decoration where the pattern is applied to the raw glaze before firing. During glost-firing the design sinks into and becomes an integral part of the glaze surface. Delftware and faïence are typical examples.

Intaglio: A design modeled in sunken relief.

Iznik: A major centre for the production of tiles and pottery in the sixteenth and seventeenth centuries. Situated on the site of modern-day Nicaea in Turkey, Iznik wares were famed for the characteristic raised red pigment, known as ‘Armenian Bole’.

Kiln: A large oven for firing ceramics. It may be fuelled with coal, wood, oil, electricity or gas. (See also: Bottle Kiln; Tunnel Kiln)

Lead-Glaze: A rich, glossy, transparent glaze consisting chiefly of various lead compounds. Usually clear, it may be stained with naturally occurring or deliberately added contaminants such as iron oxides (rich brown colors), or copper (shades of green.)

Line-Impressed (I): (medieval) A decorative technique whereby lines are impressed into the surface of the tile which is then glazed.

Line-Impressed (II): (nineteenth & twentieth century) A decorative technique whereby raised lines are molded onto the surface of the tile to resemble tube-lining.

Lock-Back: An undercut pattern molded or impressed into the back of a tile during manufacture to prevent the tile working loose from its fixing.

Luster: A vivid iridescence or metallic sheen produced on the surface of ceramics by firing metallic oxides onto the surface of the glaze in a reducing atmosphere. A thin film of pure metal is left on the surface creating a reflective surface.

Maiolica: A tin-glazed earthenware painted with ceramic colors, similar to faïence, but generally with little if any of the white tin-glaze left showing. Probably named after Majorca, a major centre for the export of such wares in the fifteenth and sixteenth centuries.

Majolica: Lead-glazed, relief molded earthenware decorated with opaque, colored glazes developed by Léon Arnoux for Herbert Minton in 1849 and first exhibited at the Great Exhibition of 1851.

Manganese Purple: A strong purple color produced from manganese ores, used mainly in faïence, maiolica and delftwares.

Mosaic: A design created from small pieces (tesserae) of ceramic, stone, glass or other materials.

Muffle Kiln: A special low-temperature kiln used for firing enamels and some lusters.

Nail Holes: Delftware tiles often have small holes in the front surface, near the corners. These are a result of the use of a wooden template board to cut the tiles to shape before firing. To prevent the board from slipping, small nails are hammered through, leaving the characteristic small holes in two or more corners of the finished tile.

Over-Glaze: Applying decoration to a tile that has already been glazed, using enamels that are fired at a relatively low temperature in a muffle kiln. This is the least durable ceramic decorating technique as the surface decoration can be rubbed away in time.

Opus Sectile: The technique of shaping tiles to follow the outlines of the design, each tile being a different shape. The technique was originally used with natural stone as a variation of mosaic. In the 1880s, Powells of Whitefriars, London, used the name to describe their own shaped glass tile compositions, and in the early twentieth century, the Porcelayne Fles Company of Delft in the Netherlands, used the name Opus Sectiel (sic) to describe their earthenware tiles utilizing a similar technique.

Pâte-sur-Pâte: From the French meaning ‘paste-on-paste’. A decorative technique similar to barbotine but using thin white slip built up painstakingly over a dark colored or stained body.

Photographic Tile: Two main techniques have been used to create tiles with a photographic image: (a) The relief molded process; pioneered by George Cartlidge for Sherwin and Cotton. A block of light-sensitive gelatin is exposed through a photographic negative for 24 hours. When the gelatin is washed with water, the areas exposed to the light are washed away leaving a relief image. From this, a mold is created from which the tiles are pressed. A special glaze is applied which runs freely in the firing, leaving the higher parts of the design showing through. The effect is that of a dark sepia-tone photograph. (b) The dusting-on process; a special print is made from the negative using a film that becomes sticky on exposure to light. Ceramic color in powder form is then dusted over the film, where it adheres to the sticky areas. This is then rubbed down onto the tile so that the image is deposited on the surface of the tile. This is then glazed and fired to fix the design.

Plastic Clay: Clay in its natural wet state, or with water added to make it moldable. Plastic clay can be cut to form flat tiles, pressed into a mold to produce relief tiles, or have a pattern impressed into it.

Porcelain: A clay body consisting mainly of the natural material kaolin (china clay), fired at a very high temperature (1250º - 1400º C, 2250º to 2550ºF.) to produce a fine white, impervious material.

Pouncing: A technique of transferring a pattern to a blank tile to aid repetitive design. The outline of the design is drawn on paper (spons) and the lines are then pricked through with a pin. Crushed charcoal is then ‘pounced’ through the holes using a small bag (or ‘pounce’) to leave a pattern of dots that guide the painter.

Prosser’s Patent: In 1842 Richard Prosser took out a patent for the manufacture of buttons and similar items using dust clay. Herbert Minton bought the patent and used it to manufacture mosaic tesserae and small tiles. He later developed the technique to make larger tiles up to 12 inches square.

Quarry Tile (UK): In the U.K., quarry tile signifies a fairly coarse, unglazed, plain colored tile used for flooring. These are traditionally made in the same way as bricks, by pressing clay into a wooden mold (slop molding), but in recent times, the term has also been applied to extruded tiles.

Quarry Tile (USA): In North America, quarry tile signifies a fine surface plain or decorated floor tile of high quality, usually dust-pressed.

Relief Molded: Tile with a pattern formed in relief from a mold or impressed design. The design can then be glazed in a single color or areas can be highlighted in different colored glazes.

Rutile Glazes: Glazes made from the ores or refined salts and oxides of Uranium, usually producing a vivid orange or red color.

Screen-printing: A piece of taut open-weave silk, metal, or synthetic fabric carries the negative of the desired image in an impervious substance, such as glue; ink is forced through the clear (printing) areas by a squeegee onto the ceramic tile or other material behind.

Sgraffito: A layer of colored slip (engobe) is applied to the top surface of a tile. The design is then scratched back through the slip to the underlying body color.

Sgraffiato: Similar to sgraffito, but the slip is cut away in broad, flat areas rather than just outlines.

Slip: Clay watered down to the consistency of thin cream. This is used to paint (barbotine), cover (engobe), or otherwise decorate a ceramic surface.

Slip-Trailing: Applying a runny slip to the surface of an unfired tile using a broad nozzle. The slip spreads out to form a broad outline. This term is sometimes wrongly applied to tube-lining.

Spons (plural: Sponsen): A pricked paper pattern from which a design is transferred to the tile surface by pouncing.

Stencil: A pierced sheet of thin metal, plastic or paper which is laid over the surface to be decorated, masking off areas to create a pattern by brush-painting or spraying with an aerograph.

Stoneware: A clay body, naturally rich in silica or with added flint, firing to a high temperature. The resultant body is impervious to moisture and therefore especially suited to external use. Stoneware bodies often incorporate a proportion of grog to improve the workability of the clay.

Terra Cotta (U.K.: Terracotta): Literally ‘fired earth’, the term is applied to coarse, unglazed floor tiles (usually red bodied), without decoration. Terra cotta is also used to describe large decorative ceramic blocks used as architectural embellishment, mainly on the exterior of buildings; sometimes structural, sometimes applied as a veneer.

Tessera (plural: Tesserae): The small individual pieces of a mosaic.

Tin-Glaze: A lead-glaze to which a proportion of tin oxide has been added, making the glaze white and opaque.

Transfer-printing: Due to irregularities of surface, it is not possible to print direct onto a ceramic surface. In 1756, Sadler and Green of Liverpool developed the technique of printing a design onto a thin tissue paper which was then rubbed face down onto the tile surface, before the ink dried. Initially the inks were made with enamel colors applied over-glaze, but these were soon superseded by ceramic colors, which could be applied under-glaze. The earliest Sadler and Green tiles were printed from woodblocks (1756), but within 6 months, they were using copper plate engravings.

Tube-Lining: A process akin to piping icing onto a cake. Slip clay is placed in a squeeze bulb fitted with a fine nozzle. As the bulb is squeezed, a thin line of clay is piped onto the surface of the tile, creating raised lines that contain and separate colored glazes that are applied after the slip has dried.

Tunnel Kiln: Invented in 1914 by Conrad Dressler, a German-born sculptor working in England, the tunnel kiln was the first continuously operating kiln. It consists of a long, square tunnel, heated at the middle, through which the tiles are transported on a train of special heatproof wagons, running on rails. Taking up to 24 hours to traverse the tunnel, the tiles gradually rise in temperature and then fall slowly back to cool, thus avoiding thermal shock.

Under-Glaze: The technique of decorating directly onto the body of the tile and then applying a transparent or translucent glaze over the design. This is the most durable method of ceramic decoration.

Zaffer: Cobalt ore used to produce a rich blue ceramic color.

Last modified 9 April 2013