Majolica - prounounce the "j" as in "jolly", is named for the Spanish island of Majorca where the production of this functional ceramic earthenware, characterized by ornate decorations over a base of white tin or lead glaze and under a lustrous clear glaze, reached its pinnacle of quality and beauty.
Matte - a glaze which has a surface that is not shiny, although it may have some sheen, ranging from dull to stony color with a slight sheen or patina.
Mature - clay that has been fired to a tight, hard and serviceable piece of pottery.
Medium Fire - firing above 2014 F (1101 C) or cone 03, up to 2232 F (1222 C), or cone 6. Typical of a firing for stoneware.
Mica - any group of chemically and physically related silicate minerals.
Mold - a hollow two piece block of plaster of paris held together with bindings. When filled with slip, let set and opened produces a replica of the design on the inside that has to be cleaned and fired.
Monochrome Pottery - this is pottery that is typically painted or glazed in different shades of one color.
Mudstone - fine grained sedimentary rock whose original make up is clay or mud or both.
Necking - The process by which a softened material deforms under pressure forming a thin neck.
Obsidian - a dark or black glass produced by a volcano. Consists of silica, heated until it flows, and then cooled. See also pumice.
Once Fired - a piece of pottery that has undergone a single glaze firing. The glaze is applied directly on to the dry or leather hard pottery avoiding the bisque firing. This approach, although offering certain economic and aesthetic advantages, can create technical problems for the pottery worker.
Opacifier - this is a substance that is typically made of a metal oxide, commonly tin oxide. When added to a clear glaze will turn the glaze opaque.
Opalescent - showing a milky iridescent color.
Opaque - a glaze that will not pass light, blocking any color underneath it, whether of the clay, a decoration or another glaze. Glazes are typically made opaque by the addition of tin oxide or various zirconium compounds.
Open - to make a clay more open or porous in structure by adding fillers or grog.
Ornamental Ware - either hand decorated by the artist or glazed with a special controlled effect. In the strictest sense, pottery and ceramics made and decorated by hand. Where casting is used the mold was usually made by the artisan. Various techniques of glazing for the finishing design will cause very different results and is a matter of choice of the pottery workers.
Overglaze - when decorations are applied to the pottery after the ghost-firing, they are known as overglaze decorations. The colors are apt to be brighter and sharper. You can identify overglaze decorations by running your finger over the pottery from the background to the decorations. If you feel a change in texture, it is an overglaze.
Oxidation - a firing where there is either no combustion occurring as in an electric kiln or where there is sufficient oxygen in the kiln to allow the fuel to burn cleanly, referring to gas, wood, oil or coal burning kilns. The atmosphere of the kiln (oxidation, or reduction) dramatically affects the resulting clay and glaze colors, for example, copper in oxidation is green (as is copper oxide) in reduction it becomes red (more like copper metal).
Oxide - any element combined with oxygen.
Paper Clay - by the addition of paper pulp to plastic clay, proportions of 50% to the total, there is greater plasticity, a reduction of shrinkage and an almost glue like bonding that occurs. This is especially important to pottery workers and sculptors when joining pieces together.
Pate-sur-Pate - (French) was first employed in China during the eighteenth century. It is the successive application of semi-fluid clay to build up a design in slight relief.
Parian - is unglazed porcelain or bisque pottery intended to resemble marble.
Patina - thin layer of antiquing stain that is applied and wiped back leaving it only in the lines of the design on the piece of pottery or ceramic.
Peep Hole - kilns have two or three sections stacked on top of each other and each section has a one inch hole that has a removable ceramic plug that can be removed to check progress of firing by looking at cones.
Pinching - indenting a pot with the fingers and thumbs before it is hard.
Pinch Pots - are pottery pots made by forming a ball of clay, and with just the pottery worker's hands pushing one thumb down into the center of the ball and pinching up the wall while rotating the pot. Simple, but some of the world's most treasured pieces of raku pottery are plain old pinch pots.
Pinholes - tiny holes that penetrate a glazed surface cause by escaping gasses.
Plasticity - the plastic properties of clay are principally determined by the size of the platelets. The smaller the platelets the more plastic the clay is. Aging or souring is also relevant to a clays plasticity and with time bacterial action creates a colloidal gel, which aids the lubrication of the platelets.
Plaster of Paris - or simply plaster, is a type of building material based on calcium sulfate hemihydrate. A large gypsum deposit at Montmartre in Paris is the source of the name. When the dry plaster powder is mixed with water, it re-forms into gypsum, initially as a paste but eventually drying into a solid. Plaster of Paris is absorbent. This feature is put to good use in pottery as working surfaces on which overly wet clay can be wedged to bring it to a more workable condition. Plaster of Paris is easy to shape and makes a great mold in which to pour slip or over which (as in hump molding) clay can be shaped into desired forms, or molds can be made to create duplicates of a statue by pouring slip into it. See slip casting.
Porcelain - is clear pottery with a body which is non-porous, non-absorbent, or vitrified. To be true porcelain, a piece should show the shadow of your hand when held before light. When a piece of porcelain is struck, there should be a clear, bell-like tone.
Porous - anything which absorbs or leaks water. In pottery and ceramics this usually refers to a clay that has been dried but not fired or fired but not to a high enough temperature to glassify it, which makes it vitreous, so that it would be non-porous.
Pugged - a term used meaning that all the air has been pushed out of the clay.
Pulling Shaping a handle.
Pumice - a porous form of obsidian or volcanic glass that is frothy, spongy and light in appearance, usually dull gray in color, formed by trapped and escaping gases in a volcano.
Pyrometric - measuring for high temperatures.
Pyrometric Bars - bars especially designed to function in a kiln-sitter, and give the same results as a centered small cone. The uniform shape makes consistent placement easy without affecting the firing. The novice will welcome the ease of use, while those practiced in firing will appreciate the consistency.
Quartz - a naturally occurring crystal of silica either in pure form or with impurities, which cause it to have a wide range of colors and finishes. Quartz is the basic constituent of sandstone and quartzite. It also often contains gold.
Raku - a method of low-fire surface change produced commonly by putting a red-hot piece of pottery into a bucket called a sagger, which contains combustible material, typically sawdust, newspaper, leaves and even garbage. The temperature of the piece ignites the materials and they begin to smoke. A lid is then placed on the bucket, producing a reduction atmosphere, along with the effects of the smoke of the burning materials. Raku can also be accomplished in a raku kiln where the piece is both fired and the raku atmosphere created.
Raku Kiln - where a piece of pottery or ceramic is both fired and a raku atmosphere created.
Raw - glaze or clay which has not yet been fired. It may still be greenware or fully dried. See also bisque and mature.
Red Clay - a term that pottery workers use to describe clay that is brown. When fired to 1832 F (1000 C) the clays will turn a deep orange color. Red clays will vitrify below 2192 F (1200 C).
Red Heat - temperature of 1292 F - 1382 F (700 C - 750 C)
Reduction - the atmosphere in a kiln which has insufficient air to support complete combustion. This will often cause smoke, which affects the surfaces of glazes and clays, and may also cause glaze or clay molecules which contains oxygen atoms to give up their oxygen to the atmosphere where it is consumed by combustible materials or other things such as sawdust or other burnable items place in the kiln. It is a condition created in a kiln in order to produce specific effects on the pottery and ceramic being fired. This reduced level of oxygen causes incomplete combustion of the fuel and raises the level of carbon inside the kiln. At high temperatures the carbon will bond with and remove the oxygen in the metal oxides used as colorants. See also oxidation and raku.
Redware - the base clay is often the determining factor for how a piece of pottery is named. It is made from a clay with a high amount of ferrous oxide, which gives the body its red color and usually has a lead glaze.
Refractory - an adjective describing any material that melts at a very high temperature.
Relief - projection of figures or forms from a flat background.
Resist Decoration - When a wax is painted onto pottery that area will resist any coloring or glaze.
Rutile - a natural ore containing titanium dioxide and a small amount of iron. Used as a slip and glaze colorant, rutile produces creams, tans and browns in oxidation and various bright oranges and blues in reduction. It tends to produce mottled or broken colors, increase opacity, and promote the growth of crystals in glazes.
Sagger - a clay pot or bucket in which pieces of pottery are placed while inside a kiln to protect them from the direct effect of flames, or a clay, sometimes metal, like a garbage can or bucket, used to hold combustible materials such as wood, paper, sawdust, etc.
Salt Glaze - by throwing salt into a kiln during the glaze firing, a shiny gloss will occur as it vaporizes and combines with the silica in the body of the pottery. Once a kiln has been used for salt glazing it can only be used for that type of firing after that.
Score - scratching tiny criss cross lines on areas of greenware that will be fastened together.
Sensing Rod - the middle moveable rod on the kiln sitter that lays on a cone and shuts the kiln off when the cone sags and lowers it.
Self-Supporting Witness Cones - visually monitor the progress of the firing and to evaluate heat work in different locations in the kiln. They are great for test firings, and are recommended by many glaze and kiln manufacturers to achieve best results. They feature a built-in base for support during firing, and require no cone holder or plaque. Correct height 1 3/4" and angle 8 degrees are built-in to help insure reproducible firings time after time. They are popular as witness cones on the kiln shelf too.
Sgraffito - this is a design that can be made by scraping or scratching through a layer of slip that has been applied to a piece of pottery to reach the contrasting color of the clay body beneath.
Shards - pieces of broken pottery.
|A small town is a place where the only automatic teller is the town gossip.