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Glossary U-V-W-X-Y-Z

UNDERGLAZE — Ceramic colors combined with clay applied under a glaze, usually a clear glaze. Although a durable method of decorating, colors can run especially if colorants, which double as fluxes, are used, however more dependable than overglaze stains. 

VENTING — The process of opening the kiln lid or door during the fusing process.

VESICA — Refers to a decorative, pointed oval design cut into a glass piece.

VETRO A RETICELLO —  An Italian term, meaning "glass with a small network." This blown glass technique utilizes glass canes laid in crisscross pattern to form a fine net, which may contain tiny trapped air bubbles.

VETRO A RETORTI — A type of glass made with canes that have been twisted to form a spiral pattern.

VISCOSITY — A liquid’s internal resistance to flowing. The ability of a liquid to flow, the term is used by the potter in relation to molten glazes, glaze suspensions, and slips. A stiff molten (liquid) glaze is one of high viscosity, while a runny molten (liquid) glaze is one of low viscosity.

VITRIFICATION — The degree of melt in a clay body as the silica forms a glass with fluxes present. The transformation of a material into glass. In pottery, vitrification refers to the changes undergone by clays and glazes when they're fired in pottery kilns. At a given temperature, the pottery surface will become vitreous, i.e. glossy or glass-like.

VITROGRAPH — The act of maneuvering molten glass as it flow from the bottom of a raised and supported kiln.

WATER —  H2O. A most important part of clay and is also used to suspend the particles of a glaze prior to application. The water in clay takes three forms; Water of plasticity, Pore Water and Chemically bonded water. Water of plasticity lubricates the clay platelets. The pore water is water of plasticity that is trapped during the drying process in between platelets of clay. Pore water can cause problems in the bisque firing even if it appears the pot is bone dry and caution must be taken up to around 150oC, 248 oF (Water smoking period). The chemically bonded water is driven off up to around 600oC, 1112 oF trailing off at 700 oC, 1292 oF henceforth it becomes ceramic. (The theoretical formula for clay is Al2O3 2SiO2 2H2O and becomes AL2O3 2SiO2 upon the ceramic change) See Clay, Firing, and Ceramic Change. 

WAX RESIST —  A decorative technique where a wax based medium is used to create a pattern, which is then covered, in another coat of glaze or slip. The wax resists the subsequent coating creating the pattern. Paper stencils or tape can create a similar effect. Latex is another effective resist with other advantages.

WHEEL ENGRAVING — The process of decorating the surface of the glass by grinding it against a wheel. The engraver holds the object against the underside of the rotating wheel to which disks of various sizes and materials and an abrasive in a grease or slurry have been applied.

WEDGING —  To kneed or mix plastic clay by hand. A hand process used to homogenize the clay and remove air bubbles, thus making it workable. The techniques for wedging are called; Spiral, or Chrysanthemum wedging, Rams head, or Monkey face wedging and wire/slab wedging. Both Rams head and Spiral wedging involves the folding of the clay on itself too build up an ever-tightening spiral of clay platelets. Wire wedging builds up increasing layers of clay platelets and is the best for introducing other clays and fillers into an already plastic clay body

Wedge Venting — Using a wedge of 1/2 inch to 1 inch to vent the kiln during firing.

Wet Felt — Soaking a ceramic-fiber with rigidizer and using it for mold making.

Wire — The act of using wire to enhance a piece of artwork.

Wire Wrapping — The act of using wire to enhance a piece of artwork.

Wire Wrapping Tools — The use of tools to bind and twist wires together. Some of the tools used include pliers and wire cutters.

Zanfirico — Italian decorative glassblowing technique.

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