There are over thirty types of clay, but in pottery these types are divided into the three main classes of earthenware clay bodies, mid-fire stoneware clay bodies and high-fire stoneware clay bodies. These three classes are sometimes described as earthenware, stoneware and porcelain, respectively, after the type of pottery these clays make.Clays fired at higher temperatures tend to be less permeable.
These categories of clay are based on how long and at what temperature the clay must be fired in order to reach maturation, or its optimal hardness. Each category includes clays with different colors and degrees of workability. Clay colors are caused by impurities. For instance, red clay generally contains a high level of iron relative to other clays, and black clay contains manganese. Clay workability refers to how plastic the clay is. Higher levels of kaolin make clays less plastic, but also less porous.
Porcelain clays have the highest firing temperature. They are made of fine-grained white clays with high levels of kaolin. Stoneware clays fire at a medium temperature and are exceptionally durable and non-porous. Stoneware clays are often buff, brown or gray due to low levels of impurities. Earthenware clays have the lowest firing temperatures, but they are often more porous and less durable. Because of the low firing temperature achievable in a simple pit fire, earthenware was the first form of fired ceramic invented by humans. Earthenware is often called terra cotta or simply pottery.Learn More
There are four principal contributors to acidic soil: rainfall and leaching, the decomposition of organic materials, the introduction of high-acidity materials into the soil and the harvest of abundantly yielding crops. The more time that passes, the more likely a soil becomes acidic and the less easily plants grow. One way the acidity of soil can be neutralized is to add lime to the soil.Full Answer >
Evergreen forests are important for the protection and sustenance they provide for a wide variety of species ranging from birds to mammals. Evergreens also provide a number of decorative and practical uses for people.Full Answer >
A fallow field is land that a farmer plows but does not cultivate for one or more seasons to allow the field to become more fertile again. The practice of leaving fields fallow dates back to ancient times when farmers realized that using soil over and over again depleted its nutrients. A three-field rotation system was used in medieval times in which one field was always fallow.Full Answer >
The primary difference between sand and silt is the particle size. Sand is composed of large particles, making it excessively coarse. Silt is made of much smaller particles and is slippery to the touch.Full Answer >