Rack - A drying device or structure for clay pieces not yet fired that allows them to dry with the least amount of distortion.
Raku - Method of firing a special Raku clay body for a desired effect.
Rasp - Hand tool with teeth rather than serrations, used for wood, stone, plaster, or metal. It can be double-ended or single ended with the opposite end attached to a handle. Teeth are hand punched and sharp. Size and coarseness of the teeth vary.
Raw Glaze - Glaze formula component without additives. These are the primary glaze ingredients such as iron oxide, ochre, etc.
Reducing - Taking a large sculpture and making it smaller using a pantograph or reversing the enlarging process.
Reducing Agent - An additive that cuts or thins a base material. For example, shellac is cut by alcohol before applying to a model in mold making.
Reduction Firing - Firing process whereby oxygen is regulated to create a special effect on the fired clay or glaze.
Refractory - Material fired to a high enough level to withstand the high temperatures of firing in a kiln used for shelves and posts.
Regulator - Device that controls the flow of a material into a mold.
Reinforcement - Addition of metal or wood cross sections either on the outside of a mold or in the casting of delicate pieces where extra strength is required.
Relief - Flat one-sided sculpture, also called bas-relief.
Resin - Plastic liquid material designed for casting into specially constructed rubber that can withstand the heat of the curing process.
Respirator - Safety device worn over the nose and mouth to protect the lungs from harmful dust or vapors. Available in a variety of materials and designs.
Retaining Wall - Fence that separates sections of the mold; outside area on a relief mold that restrains mold making material to a given area. Constructed of various materials such as wood, metal, clay, or plastilina.
Rib - Tool used primarily by potters for shaping wet clay that has been thrown on the wheel. Can also be used for leveling or scraping.
Riffler - Small rasp type tool with fine serrated cutting edges used for finishing stone and wood. Also known as a jeweler’s rasp.
Rod - Used to strengthen internal sections of a cast. The rod should be non-corrosive so rust will not bleed through the final casting.
ROMA - Trade name of Sculpture House, Inc. Italian formula plastilina made in the United States using the highest grade materials available. Oil- and wax-base modeling material preferred by professional sculptors.
Roman Joint - Square locking section on a model or mold to keep it from shifting. Used by professional mold makers and casters, it is the most difficult joint to make.
Roman Wax - Hard casting wax used for the investment process in the lost wax casting process. Color may vary from purple to black but its brittleness will remain the same. Usually used for fine detailing before casting rather than for direct modeling.
Roughing Out - Creating the basic geometric form from a large natural piece of wood or stone; also applied to clay and plastilina.
Rondel - Round cape-shaped stone carving tool.
Royal Porcelain - Trade name of Sculpture House, Inc. Porcelain clay formula containing English China clay made exclusively in the United States. Clay is fired at cone 10-12 and produces a translucent effect. It is the most difficult clay material to throw or fire due to its delicate nature.
Running - A build-up of glaze that flows beyond desired boundaries. Also known as pooling.
Running Plaster - Liquid plaster poured before the material sets.
Rust - Reddish coating formed on metal that contains iron, caused by moisture. Rods that are galvanized, when inserted into a cast will sometimes rust through the cast plaster piece.
Rutile - Brown, deep red, or black mineral that gives a brilliant metallic luster to ceramics and pottery when fired in a glaze.