Q: What is the difference between low fire and high fire clay?
Low fire and high fire are relative terms that relate to breaking up the vast range of firing temperatures that are most often used in ceramics. In very basic terms low fire clay is referring to clays that are often: earthenware, terra-cotta and/or sculpture formulations; where as the term high fire is usually used in describing: stoneware, dinnerware and porcelain clays.
Q: What happens to clay when it gets old?
As clay ages or gets old several characteristics can manifest themselves some good and some less desired depending on the type of clay and state of aging. In general after initial mixing and packaging has taken place, continued wetting down of clay particles occurs until complete saturation of the fine granules from the available water thus making the clay more plastic and workable. If a wet prepared clay is stored in a cool or damp environment, this clay can keep and be ready to use, with very little added preparation, for periods of more than a year to eighteen months. If clays are not properly stored and are allowed to dry out the resulting product is not useless but rather less desirable to use. Clay until it is fired never goes bad. it is one of the most recyclable materials in nature. With the proper addition of both water and time any clay can be ready to use and reuse.
Q: What happens to clay when it freezes?
Freezing of wet clay does not completely damage the clay. However it does make it less desirable to use immediately after thawing. The act of freezing drawing water molecules from inside the clay block and freezes as frost and forming ice crystals on the out side surface of the clay but inside the plastic packaging. Upon thawing the ice melts and water gravitates to the low resting point of the package, leaving the dense block of clay drier and crumbly in the top and center and a disproportionate amount of water at the bottom and edges of the unit. Over time capillary action will redistribute the moisture but generally not soon enough for the user unless kneading and wedging techniques are implemented.
Q: What is slip?
Slip or casting clay is an high wet down mixture of clay, water and other essential ingredients often used to create thin walled vessels, figurines and other voluminous shapes using ceramics and plaster molds. Casting slip can be formulated for many uses ranging in temperature, color and strength. We offering both earthenware and stoneware slip.
See Casting Slip
Q: Do you have a short and easy introduction to slip casting?
Actually, one of our employees, Rich Juckel, has written a published article on slip casting. Click below for a printable pdf version.
Q: What kind of clay can I use for outdoor walkways, tiles and sculptures?
The common characteristic in all of these desired applications is strength. Strength is obtained in any clay formulation when it is fired to its upper end or near vitrification range. Vitrification is a term used to describe a material becoming impervious or impenetrable to a another material such as water or oil. Because outdoor applications expose clay to sometimes harsh and abrasive conditions, special consideration has to be evaluated before choosing a clay. No matter what its material composition is, the determination of whether a fired ceramic product can be used in specific installation or application: the final say of acceptability is left to either the architect, builder, installer, municipality or local building code.
Q: What's the difference between glaze and underglaze?
Glaze is a blend of powdered chemicals and minerals mixed with water and applied to clay. When fired to the glaze's maturation temperature it melts and becomes a thin layer of colored glass that fuses to the clay and acts as a decorative and utilitarian surface on the clay.
Underglaze as conveyed in its name is a similar blending of minerals as in glaze with the addition of clay and other less melting components along with a greater content of color producing chemicals that allow the user to do more detailed decoration on the clay surface before applying a usually desired protective layer of glaze on top of the underglaze. Separate firings of underglaze and glaze is NOT always necessary but may be advantageous in extremely detailed underglazing applications.
Q: Why did I get bubbles in my glaze?
Bubbling in glaze can arise for several reasons. The first can be caused by physical air that was trapped during application and not allowed to escape in the glaze firing because the firing was too fast or not fired hot enough. A glaze application that is not thick enough can also cause bubbling.
Q: Why did I get blisters in my glaze?
Blistering in glaze is most often attributed to over firing and or too thin of a glaze application. It can be the result of a firing that has been completed and the retained ambient heat provides additional boiling or out-gassing of the glaze while the local air is already cooling the glaze on the suface.
Q: Why did I get pinholes in my glaze?
Pinholing results in glaze from bubbling or blistering that was not allowed to settle down in the glaze firing cycle. Corrective steps that can be taken include multiple thinner glaze applications rather than one thick single application, avoid over-firing, and applying a heat soaking procedure at the melting high end of the firing can help allow any remaining gas to escape before hardening upon cool down.
Q: What is engobe?
Engobe is an American term for decorative slips used for simple and basic color decoration. They are essentially the least complex formulas of the underglaze family. Because of there simplicity they are generally required to be applied to either semidry or leatherhard clay. The higher clay content in engobes often limits the color selection to basic shades that oxides provide.
Q: How do I get bright red/yellow/orange glaze? Why are these colors hard to get and so expensive?
In ceramics bright reds yellows and orange colors are most often obtained by materials containing either lead, cadmium or both. Cadmium is considered a fragile/elusive metal in ceramics and has always required plenty of oxygen in order to retain any color as a result of combustion. Recently innovations have been made in the metals and pigment processing that helped stabilize cadmium colors. They are commonly referred to encapsulated stains.
Q: Do I need to wear a mask? When?
See Safety Items
Q: How can I make a mold?
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Bat Mold and Slump Hump Directions
Plaster Mixing Instructions
WHEELS AND THROWING
Q: Does Continental Clay have used wheels?
Continental Clay periodically has used wheels available for sale. Upon arrival wheels receive an assessment then either get the necessary tune up or a company backed stamp of approval before sale to the public.
KILNS AND FIRING
Q: Does Continental Clay have used kilns?
Continental Clay periodically has used kilns available for sale. Upon arrival kilns receive an assessment then either get the necessary tune up or a company backed stamp of approval before sale to the public.
How do I apply kiln wash?
Printable Kiln Wash Mixing and Application Instructions
Q: Do I need a kiln vent?
Kiln Vent Information