Definitions

Absorbency

The uptake of liquids into the voids of porous materials. Ceramics with low absorbency are generally stronger than ceramics with high absorbency.

Ball-end Tool

A Ball-end end mill has a hemispherical to spherical form. These mills are used in a number of milling processes from cutting and shaping to reducing stress concentrations by eliminating right angles. These mills have a cutting profile similar to a meniscus, or half circle. When used to direct mill a mold, the resulting cast surface will have concave ridges.

Biscuit

A low-fire process in which moisture is removed from clay particles, which fuse together to create one ceramic mass. The clay particles undergo a physical and chemical change.

Blackhard

The portion of the drying process where the clay is not fully dried, however is no longer malleable.

Casting Slip

A clay-water mixture used to create ceramic forms from porous molds. The final form of the ceramic object is achieved by casting the slip into a mold, which draws moisture out of the slip. After achieving the proper thickness, the cast form is removed from its mold, glazed, and fired. Tectonic Horizons was created using Casting Slip, and the Slip Cast technique.

Ceramic Change

The point at which the temperature of the ceramic mixture is great enough to physically drive off chemically bonded water molecules from clay particles. The change generally occurs between 1000 - 1200 F. The higher the temperature the greater the durability of the final object will be.

Ceramics

Clay objects stabilized through the application of heat. The advanced fabrication of ceramics is the focus of this site.

Clay

A naturally occurring inorganic substance composed of very small "plate- like" particles. These particles, when mixed with water as a lubricant, can slide past each other with relative ease. Known as "plasticity" or "workability", this gives clay its unique characteristic.

Claybody

A mixture of clay and various compounds used by ceramicists to achieve varying characteristics of final ceramic objects.

Computer Numeric Control (CNC)

A process by which a machine, typically a mill, is guided along tool-paths by a computer to produce a geometry generally created in a 3-D modeling environment.

Flat-end Tool

Flat-end tools, commonly referred to simply as end mills, are tools with a flat end, providing a straight cutting profile. Flat-end tools are used for plunge drilling as well as lateral cuts.

Leatherhard

The point in the drying process when a clay object can be handled without the significant deformation of the shape. At this stage the clay is still pliable enough to be altered if necessary.

Milling Tools

The router bits used for reductive CNC milling.

Plaster Bat

A simple slab of plaster often used for drying purposes so that wet clay pieces can try more or less uniformly as air dries all exposed surfaces except for the bottom surface which is dried by the plaster underneath absorbing moisture. Plaster bats can also be used as flat mold parts for slip-casting.

Plaster Blank

A block of plaster cast to the approximate dimensions of mold part geometry to be digitally milled. Plaster blanks should be cast with care to introduce as few air bubbles as possible.

Plaster Mold (for slip casting)

A plaster mold used for slip casting will slowly degrade over time as water is absorbed into (and through) the plaster mold. Molds can typically be expected to produce approximately 100 casts.

Porosity

The ability to absorb water by capillary action.

Positive

A positive (also called a model or pattern) is the form from which negative molds are cast. Casts from these molds will then be copies of the positive model. Positives can be produced by hand crafting clay, plaster, wood, or other materials as well as through CNC machining and printing techniques.

Scalloping

Scalloping is the term used to describe the material left on the machined form due to the size of the step over. An infinitely small step-over results in virtually no scalloping, however increases the milling time for the object in question to undesirable amounts. A Large step-over results in a lot of scalloping, which will have to be finished by hand, delaying project completion.

Shrinkage

An irreversible reduction in the size/volume of a ceramic piece or glaze which is caused during the drying and firing process. This differs from expansion and contraction, which occurs naturally as a piece heats and cools. All pieces usually undergo a small amount of shrinkage. It takes a lot of experience and skill to select and work with the right types of clays and glazes so that shrinkage does not deform or otherwise damage a finished piece.

Step-over

The spacing between each milling pass. A tighter (or lower value) step-over produces finer, smoother resolution. The lower the step-over, the closer the manufactured geometry will approximate the digital geometry. Depending on the size of the piece, lowering step-over can increase the milling time.