Tech Tuesday: Clay Body Vocab
- , by Haley Stanaford
- 3 min reading time
Clay is tricky! There are a lot of concepts and words that get thrown around in conversation and it’s hard to keep up with all these things! Here are some words that may come up in conversation when talking about clay bodies.
This article is (sort of) a threequel (is that a word?) to my other articles Raw Material Vocabulary and Glaze Vocabulary. Those articles do not have to be read to understand this one, they just provide supportive and additional information.
Greenware
Greenware are pieces that have not been fired yet. Sometimes these pieces are referred to as “green”.
Bisqueware
Biqueware are ceramic pieces that have been bisqued, meaning they have been fired for the first time.
Flux
Fluxes are the melters. In clay, the melt is the reason clay can be fired to be more vitrified (read more about vitrification in my other article here). The melt reduce porosity and water absorption in the clay body.
Plasticity
Clay is a material that is able to stretch and be molded. This concept is referred to as plasticity. Some clays are more plastic than others so they can be used in different ways.
Short
“Short” is a term used to describe clay bodies that have little plasticity. You can tell if your clay is short by rolling it into a coil and wrapping it around your finger. If the clay cracks a lot or breaks, it is short.
Bentonite
Bentonite is an additive to clay bodies that can add plasticity. Bentonite is the most plastic raw material and can solely provide plasticity to short clay bodies without messing with the chemistry of the clay body. An addition of 2-5% will do wonders for a clay body. However, bentonite must be mixed with water prior to adding it to a mixture.
Shrinkage
Pretty much all clays shrink! Clays will shrink at different points in the making process: wet to dry, green to bisque, bisque to glaze fired. Different clay bodies have different shrinkage rates but a pretty typical shrinkage rate from wet to glaze fired is 12%.
Grog
Grog is a kind of aggregate that can be added to clay bodies to help with structural strength and shrinkage. It is especially useful in sculptural clay bodies. You can read more about it here. Grog is not the only thing that can be added to clay bodies to help with structure and shrinkage. Paper, fibers, mullite, and Mulcoa are all additions that serve similar purposes and you can read more about them here.
Slip
Slip is watered down clay. Slip is used widely for slipping and scoring to join clay pieces together but it is also used for slip casting. However, slip casting slip and regular watered down clay slip are not the same thing. Slip casting slip, commonly referred to as casting slip, is a specific recipe to allow for the slip to be poured into molds and set up into their shape. Casting slips will include other ingredients to help with that process.
Bloating
Ah. Bloating. Bloating is something that happens to a clay body when it is overfired. It appears as large bubbles in the ceramic that weren’t there prior to firing. Bloating is very common in black clay bodies when fired to a cone 6, but can be seen in any clay body.
Image from digitalfire’s page on bloating
Haley Stanaford is currently a Post Baccalaureate student in ceramics at the University of Kansas where she is currently taking a Clay and Glaze Formulation taught by Colby Charpentier in addition to her studio practice. She also is a Sales Representative at Bracker’s Good Earth Clays in Lawrence, Kansas.
