Clay—the raw material which is the vessel—is the first thing you consider. There are infinite compositions of clay all around the world. Each has its own properties, and testing is the only way to determine suitability. ‘Maturity’ or ‘Mature’ is the term for completely vitrified clay, which makes the vessel impervious by high firing. The pores of the clay are as tight together as possible, making any liquid penetration impossible. A ‘clay body’ is a combination of different types of clays to give the desired attributes of the end product. Not every clay is suitable for every use.
‘Earthenware’ is the term used when referring to a low-fired clay, (1800-1900 degrees Fahrenheit) typically seen in cultures where the cost of high-firing is prohibitive. It has not matured, the clay body is open and porous, making it somewhat fragile. Very often, the glaze is lead-based because of the low melt point of lead and typically brightly colored. Those not familiar with the terms erringly equate ‘earthenware’ with all clay bodies.
‘Stoneware’, fired much hotter, matures in the range of 2280-2345 Fahrenheit, and is much denser, and much harder than earthenware. Earthenware would melt into a puddle in the kiln at these temperatures. Specific minerals from the clay deposits affect the whole and are inherent in the clay. These natural occurrences are embraced and celebrated by the makers at Earthborn Studios, who use a high-iron bearing clay body. The iron interacts with the glazes, giving them a warmth available in no other way. Speaking of glazes…
Glaze—the glass coating covering the clay. The ‘skin’ of the vessel is glass. A very specifically formulated glass that conforms to the vessel itself. Think of it as a cake recipe of earth ingredients. Silica is the glassifier, and the remaining elements affect the melt, the color, the transparency, the reflectivity, and the adhesion to the clay. The coefficient of expansion is the most critical element in the longevity and durability of a vessel. The two materials—clay and glaze—must shrink at the same rate. If not, the tension between the two will eventually manifest in a spontaneous crack, or even complete breakage. It may take months for this to show up. Telltale small cracks in the glaze, or ‘crazing’ could hint at this situation. Crazing will allow liquids to penetrate, and as such, should be avoided for culinary use.
While these are two of the most important elements of functional pottery, you’ll want to notice the thickness of the walls of the vessel, which should be consistent throughout. Uneven walls subject the vessel to stresses when heated, and the thinner will heat more quickly, and get hotter than the thicker areas, leading to possible thermal shock because the heat is not delivered evenly.
When you consider pottery for food service or home use, consider a company like Earthborn Studios who has been making dishes for chefs since 1997.
Distinctively organic, Earthborn Pottery is restaurant sturdy and beautiful. From cups to bowls to plates to serving dishes, each piece is created to chefs specifications.
