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Grigsby, Leslie B. (Leslie Brown) / The Longridge collection of English slipware and delftware. Delftware
Volume 2 (2000)

Glossary,   pp. 492-493

Page 492

For tihe informalion for entries in this glossary, 
the author heavily relied on Freestone and 
Gainister, eds., Pottery in the Making, 
pp. 214-216 
Applied decoration: Decoration created by 
   adding hand-formied or molded clay compo- 
   nents to the surface of a pot. 
Biscuit firing: The firing used to harden a clay 
   body that has not yet received its glaze nor, 
   in some cases, colored decoration. 
China clay: See Kaolin. 
China stone: Also known as porcelain stone. 
   A rock clomposed of quartz and alkali 
   feldspars that is ground for use as a 
   porcelain flux. 
Clay: A fine-grained, natural material that, 
   when wet, is characterized by its plasticity 
   (the ability of the clay to be manipulated 
   and shaped without cracking). Additives are 
   used to alter the properties of the clay 
Cobalt oxide: A pigment used under, over, or 
   suspended in ceramic glaze to achieve a 
   color ranging froim pale to deep blue. 
Combing: On slipware a type of decoration 
   created by dragging a comblike tool across 
   a patterned slip (see below) sinrface. 
Copper oxide: Used since ancient times as a 
   ceramic and glass colorant. Copper oxide 
   fires to green when fired in oxidation (see 
   below) with a lead or tin glaze. 
Delftware: Name, after prolific Dutch potting 
   center at Delft, Holland, for English tin- 
   glazed earthenware (see below). Same name, 
   sometimes with an uppercase 1), also used 
   for Dutch versions of the pottery. 
Earthenware: A ceramic body usually formed 
   of buff to red clay that is not fully vitrified 
   (see below) when fired and thus remains 
   relatively porous. Iarthenware clay can be 
   dug and used with little refinement in some 
   cases or, for more elegant wares, can be 
   highly purified. 
Enamel: A type ofi decorative pigment con- 
   posed of a metallic oxide and a glass flux 
   that is painted over a fired glaze and com- 
   pleted in a low-temperature firing. 
Fabric: The combination of clay and inclusions 
   that makes the ceramic. 
Faience: In the context of this publication, 
   the French term for tin-glazed earthenware, 
   a translation of the name for the Italian 
   potting center of Faenze. 
Firing: The heating to a high temperature of 
   clay bodies in order to render them hard, 
   durable, and no longer soluble in water. 
Firing temperature: The highest temperature 
   attained during the firing of a clay body, 
   glaze, or, in some cases, decoration. 
Flint: A very fine-grained and popular source 
   of silica, often ftund as large nodules in 
   chalk and limestone deposits, 
Flux: A substance added to a clay or glaze to 
   lower its melting temperature. 
Glaze: A thin, silica-rich, often transparent 
   layer on the surf ace of a ceriamic body 
   (see Salt glaze, Lead glaze, Tin glaze), 
Inclusions: Large-grained particles in a clay 
   body, soinetimes indicating that the clay 
   was little refined and sometimes added to 
   reduce shrinkage or firing temperature. 
Iron oxide: The most common oxide allecting 
   the fired color of ceramic clay, a strong col- 
   orant that results in earth tones when fired 
   under a lead or salt glaze in oxidation (see 
   below). Also used as a very effective flux. 
Kaolin: Another name for china clay, a 
   material that is highly refractory and rich 
   in the mineral kaolinite. Kaolin deposits, 
   comparatively rare and dilffring in quality, 
   are known from Asia, Ecurope, England, and 
   North America. These white-firing clays are 
   low in iron oxides and fluxes (see above) 
   and tend to need other materials in the mix 
   to increase their plasticity (see below). 
Kickwheel: A potter's wheel (see below) that 
   has a large, weighted circular base that is 
   turned by kicking with the foot. 
Kiln: The structure within which pottery is 
   fired. At the bottom is the firebox, in which 
   the fire is set and from which one or mcore 
   flues carry the heat into the firing chamber, 
   where the pots are stacked. A vent cirl the 
   loss of waste gases is typically at the top of 
   an updraft kiln. 
Lathe-turned: See Turning. 
Lead glaze: A glaze that melts at a compara- 
   tively low temperature (around 840' C.) 
   and for which the main flux is lead oxide. 
   Known from ancient times, lead glaze 
   usually was applied as a powder or in 
   suspension in water and, as it cannot 
   tolerate the high temperatures needed 
   to complete stoneware or porcelain, was 
   used on earthenware bodies. 
Majolica: the Italian term for tin-glazed earth- 
Manganese oxide: A relatively common metal 
   oxide that fires in oxidation (see below) to 
   black, brown, or purple. 
Modeling: The shaping of a piece of clay will] 
   the fingers or with any of several types of 
Overglaze decoration: Decoration. sometimes 
   in colors that cannot withstand glaze-iring 
   teimiperatutires, that is applied to the surface 
   of the finished glaze belore being completed 
   in a comparatively low-ieilierature firing. 
   Alternatively some color ornament and gild- 
   ing cat) be applied over the glaze and 
   adhered with an adhesive rather than 
   through heating. 
Oxidation firing: Firing in a kiln atmosphere 
   where there is excess oxygen, so that iron 
   oxides tend to forln red hemiatite rather 
   than black magnetite and carboon is burnt 
   out of the clay body. Typically produces red- 
   dish pots in low-temperaturce earthenware 
Press molding: Forming soft clay by pressing it 
   in or over ai mold. Press-molding clays must 
   be somewhat plastic biat must shrink or 
   warp comparatively little when drying. 
Porcelain: A highly vitrified (see below), usually 
   white ceramic that is translucent when 
   thinly potted and can ring when struck. 
Porcelain stone: See China stone. 
Potter's wheel: A rapidly rotating device com- 
   posed of a circular, flat table on a rotatable 
   axis, enabling the potter to use centrifugal 
   force to shape pottery. (See Kickwheel.) 
Reduction firing: Firing in a kiln where there 
   is a shortage of oxygen. Metallic oxides 
   produce different colors in reduction firing 
   than they do in oxidation firing. In redcc- 
   tion firing, for exaimple, copper oxide pro- 
   cluces red rather than green. 
Saggar: A protective ceramic container, typi- 
   cally of fireclay, used in the kiln to protect 
   glazed or other pottery fromn damage from 
   fire, gases, or contact with other pots dur- 
   ing firing. 
Salt glaze: A glaze produced when salt is 
   shoveled into a heated kiln, vaporizes, and 
   creates a chemical reaction with a ceramic 
   body. The high teimperature needed for salt 
   glazing makes it suitable fir application to 
   stoneware bodies. 
Sgraffito decoration: A type of slipware orna- 
   ment for which designs or inscriptions are 
   cut through slip (see below) to reveal the 
   body color below. 
Slip: A syrupy mixture of fine-grained clay and 
   water that sometimes forms a surface coat- 
   ing tfr slipware. Applied as a suspension of 
   fine clay particles in water. Slip ornament 
   may be applied by dipping the pot into the 
   suspension, carving, trailing through tubes, 
   combing, mixing (marbling or joggling), or 
492 The Longridge Collection 

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