Physical Stages of Clay
Clay ware takes on varying physical characteristics during the making of pottery.
- Greenware refers to unfired objects. Clay bodies at this stage are in their most plastic form. They are soft and malleable. Hence they can be easily deformed by handling.
- Leather-hard refers to a clay body that has been dried partially. At this stage the clay object has approximately 15% moisture content. Clay bodies at this stage are very firm and only slightly pliable. Trimming and handle attachment often occurs at the leather-hard state.
- Bone-dry refers to clay bodies when they reach a moisture content at or near 0%. This will occur after glaze firing, when that is done, or after biscuit firing in the case of once-fired pottery.
- Biscuit refers to the clay after the object is shaped to the desired form and fired in the kiln for the first time, known as "biscuit fired". This firing changes the clay body in in several ways. Mineral components of the clay body will undergo chemical changes that will change the colour of the clay.
- Glost fired is the final stage of some pottery making. A glaze may be applied to the biscuit form and the object can be decorated in several ways. After this the object is "glost fired", which causes the glaze material to melt, then adhere to the object. The glaze firing may also harden the body still more as chemical processes can continue to occur in the body.
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