RAKU — A lowfire form of pottery where the pots are removed from the kiln as soon as the glaze has melted and then left to cool or doused with water. In the mid 20th century Paul Soldner introduced the now popular process of post firing reduction. In this case the red hot pot is placed in a lidded bin filled with straw or sawdust. The glazes are dramatically altered by the reduction particularly noteworthy are the colors achieved with Copper.
RAKU KILN — A specialized type of kiln in which pottery items are removed while still very hot and then quickly subjected to some form of thermal shock, i.e. intense cooling. This process causes small but structurally sustainable cracks in the pottery surface, an effect known as crackling or crazing. Raku kilns are small and designed for easy accessibility to their contents.
RAMP TIME, RAMP SPEED — The time required for the kiln temperature to increase or decrease. The amount of time stated in each step of a firing schedule for your kiln to go from its current temperature to the next indicated set point, in consistent degrees per minute.
RAMPS — This term refers to the rapid heating cycles.
REACHING TONGS – Stainless steel tools that are used to reach far into your kiln to put in or remove items. They are also great for picking up and working with hot items in the kiln. They have serrated tips that help in grabbing your item.
REDUCTION FIRING — a reduction atmosphere within a pottery kiln occurs when there isn't enough oxygen to fully consume the fuel. This is done in gas kilns by reducing the draft, but isn't practical in the oxygen-rich atmosphere of electric kilns. Reduction firing results in pottery with unique color characteristics and subtler, earthier, richer colors.
REFRACTORY — Any material that will not burn, bend, warp, deform or explode at a specific high temperature.
RETICELLO — Italian decorative glassblowing technique.
RILGAREE — A form of appliquéd glass decoration in a crimped, a ribbon-like highlight on some Victorian art glass pieces.
RIIGIDIZER — A chemical added to certain ceramic fibers to bind them into a solid state.
RING MOTTLE GLASS — An opalescent glass in which rates of crystal growth have been controlled to create ring-shaped areas of opacity. The effect is a visual surface mottling.
RIPPLE — A surface texture, often dramatic, consisting of linear or irregular ripples. Created naturally in some sheet-forming processes, imitated with an embossing roll in others. This classic texture combines the light diffusion of a Granite texture with the motion of undulating lines. An irregular, wavy line pattern makes this glass the optimal choice for pieces that require strong texture.
RODS — Used to describe cylindrical, pencil-thick sticks of glass used primarily in flameworking and glass bead making. They are available in a wide color range and many expansion coefficients.
RONDEL — A mouth-blown piece of glass that has been spun into a circular shape, often irregular. Sometimes incorporated into leaded glass artworks. Machine-made facsimiles are common, called "pressed rondels."
RUN — When the glass begins to break at one edge and runs to the other edge.
RUNNING PLIERS — Used to control the breaking of the glass. They are placed on the score at the edge of the glass.