June 20, 2024

glossary of terms

Ambient Lighting
Peripheral lighting, intended to throw light behind/around and object, as opposed to fully illuminating an area.

An early plastic developed in 1907–1909 by Dr. Leo Baekeland. Valued for its electrically nonconductive and heat-resistant properties, it was used in radio and telephone casings, electrical insulators, and lamp switches/sockets.

Ball Clay
Together with other materials, ball clay is a common raw material for many ceramic articles, and is valued for its high plasticity and durability. The essential component of most types of pottery, it is used in both clay bodies and glazes. The primary sources for ball clay in the U.S. are Kentucky and Tennessee.

Beehive Kiln
A common style of kiln in the first half of the 20th Century. Cone-shaped and often coal fired, they were replaced by shuttle and tunnel kiln that were more suitable for mass production.

Bisque, or biscuit, pottery is a fired piece of unglazed ceramic. This is usually a preparatory step that is followed by re-firing with a final glaze.

Block and Case
A “pattern” made from the Master Mold, often made of a cement material called Ultracal. The block and case is used to make the Production Molds.

Also called slip casting, this is the most common process for the high-volume manufacture of pottery. Liquified clay, called slip or slurry, is poured into a mold that defines the form prior to firing.

Plaster. A preparation of sand, lime or gypsum, and water used to cast lamps and other products. As compared to ceramics, chalkware/plaster manufacture is less expensive and requires less equipment, as no high-temperature kiln is used. Both the painted finish and the body of chalkware lamps are less durable than their ceramic counterparts.

Cold Paint
In contrast to using colored glaze that is applied and then fired in a high-temperature kiln, some potteries applied color details after firing the piece. This was done with paint, typically an enamel. Much less durable than glaze, it was sometimes more cost-effective and easier to manipulate than certain glaze colors, particularly red. Lamps notwithstanding, McCoy Pottery Co. frequently applied cold painted details to their products.

Copyright (symbol, “©”)
A set of exclusive rights regulating the use of a particular design or information, attributes that are today often called “intellectual property.” Not applicable to general concepts, copyrights apply instead to specific designs/characteristics.

A fine crackle that develops over time in the glazed surface of vintage pottery. Ceramic ware that is fired at higher temperatures, like porcelain, are less prone to crazing.

The Canadian Standards Association. An organization that approves the safety of manufactured products, much like Underwriters Laboratories in the U.S.

Decorating Kiln
Small kiln that fire at a lower temperature than standard production kiln, somewhere around 1300 degrees fahrenheit. Decorating kiln are used for firing overglazes, gold decoration and transfers (decals).

Clay fired at lower temperatures, never reaching the point of vitrification.

The removal of the seam left by the mold in slip casting with a fettling knife. The seams in then finished with a sponge.

Ornate, delicate ornamental work in metal. Most of the “half-donut” style of planter/lamps are set in a plated metal base that could be described as a filigree base.

A screw-on fastener, usually decorative and sometimes matching the particular lamp, that secures a lamp shade to the harp.

Fire Brick
Insulating bricks that are used in the construction of kilns, capable of withstanding the high temperatures without deformation.

Firing Cones
Often used in sets of three, firing cones, aka pyrometric cones, are positioned in the kiln along with the wares to be fired. They, through softening and subsequent bending, provide a visual indication of when the wares have reached a required state of maturity, a combination of time and temperature.

Firing Crack
A production flaw. They occur during the firing of a ceramic piece, and can usually be distinguished from cracks caused by impact. Firing cracks often appear to be spread open slightly, and the glaze will look to have pulled away from the crack. Vintage pottery found with firing cracks were typically sold as “seconds” or taken home by a pottery employee. Such production flaws are less detrimental to value than damage resulting from rough handling.

Flea Bite
A loosely-defined term used to describe small chips in ceramic glaze.

A vitreous layer fired on a piece of pottery. This coating is what typically gives ceramic products their gloss and color.

Glaze Pop
A production flaw sometimes found on the glazed surface of pottery. It is the result of air bubbles present in the glaze at the time of firing.

Glaze Skip
An area on the ceramic body on which the glaze did not adhere, leaving an exposed “bisque” area. Usually the result of an air pocket present during the application of the glaze.

Clay products that are in the leathery state prior to firing are said to be greenware.

A metal hoop, usually oval in shape, that mounts to a lamp and supports the shade.

An oven, typically constructed of of brick, that is used to fire ceramics. This high-temperature process transforms the clay, creating a strong, but brittle, finished product.

Kiln Car
Carts that are loaded with pottery that is in the unfired greenware stage, the cars then entering the kiln for firing.

The Leviton Manufacturing Company. Founded in 1906, they were the dominant manufacturer of electrical sockets and switches throughout the 20th Century and are active today.

Italian ceramics decorated with an opaque tin-oxide glaze. The term is often loosely applied to all sorts of colorfully glazed pottery.

Master Mold
A plaster mold that is pulled directly from the original clay model of a lamp or other item. The master mold is the basis for the block and case or mold case that is in turn used to make the production molds.

Mold Case
see: Block and Case.

see: Chalkware.

Vitreous (glass-like) ceramic ware. Produced with high firing temperatures (around 2,650 degrees fahrenheit), porcelain products are extremely hard, brittle, and possess a low permeability to liquids. Porcelain typically has a high-gloss finish, but bisque porcelain is also made.

Production Mold
Plaster molds that are directly used in the manufacture of ceramics. Production Molds are created from the Block and Case and must be periodically replaced to maintain the quality of the finished products. Items made from worn production molds are characterized by a loss of detail and general “softness” of form.

Registered (symbol, “®”)
Indicates a registered trademark. Trademarks are used by an individual, business or other legal entity to identify the source of its products and/or services to consumers, and to distinguish them from those of other entities.

Pottery items that are not considered to be up to the required level of quality. Such pieces that are not suitable for sale are referred to as “seconds” and were either sold as inferior items, taken home by an employee, or destroyed.

A common term in regards to conventional lamps, it is also used to describe a piece, often fiberglass, found on some TV lamps that is used to diffuse the light.

Shuttle Kiln
A production kiln that utilizes two kiln cars. Once the firing cycle is completed, the first car is pushed out by the second. The cars are either pushed, cranked or electrically powered, and are “shuttled” back and forth. The cars are stationary during firing, the gradual heating and cooling controlled by modulating the temperature at the source. Lamp bases/TV lamps would typically be fired at around 2300 degrees F.

Slip (Slurry)
A fluid clay mixture, typically used in the ceramics industry for making cast wares. Molds are filled with slip, usually with hoses fed from the slip tank, the excess then poured out. The remaining slip (adhering to the inside of the mold) forms the body of the piece, which is then fired.

Terra Cotta
A porous red clay fired at earthenware temperatures.

Tunnel Kiln
Tunnel Kiln are typically quite large, and are essentially a long, open-ended tunnel with a centrally located heating area. The kiln cars pass through very slowly, allowing for gradual temperature changes as they get closer to, then further from, from the central firing area.

TV Lamp
Decorative back-lit lamps that saw a brief period of popularity, mainly from 1950 until the early ’60s. They were concieved during the time that television was becoming commonplace in the home, targeting fears that TV viewing, particularly in a darkened room, could damage eyesight.

see: Underwriters Laboratories.

A low-absorption gypsum cement used to make mold cases.

Underwriters Laboratories
An independent, non-profit product safety certification organization. They have certified electrical products in the U.S. since 1895.

Vitreous China
Pottery that is fired at high temperature to form a strong, non-porous body. The ceramic glaze is fused to the body, resulting in a hard, often glass-like finish.