Everything You Ever Wanted to Know About Clay – Kinderart
Here you can read about what clay is, where to find it and how to work it.
by andrea mulder-slater
what is clay?
Clay is a special type of soil that is formed by the decomposition of rocks through the action of the weather.
what does that mean?
well, basically, over time, water carries pieces of land from one place to another and deposits them in areas where the water is reduced to a trickle. (Have you ever gone digging at the water’s edge only to grab a handful of dung? Well, that dung is clay.) As the pieces of dirt travel with the water they pick up all sorts of things and by the time we pick up a box of clay from the pottery shop the dung has been collected and prepared for us to use. All the little rocks and lumps have been removed and sometimes some additional materials such as sand are added to create the perfect workable clay.
clay can be found anywhere, but it is only useful for pottery if it has good “plasticity”. you can test this by seeing how elastic a piece of clay is. if you can take a piece of clay, roll it into a coil, and fold it into a ring without it cracking or falling apart, chances are you’ll make good pottery and sculpture.
Natural clay found outdoors generally needs to be cleaned and refined before it can be used. Little rocks and lumps are removed and sometimes some additional materials such as sand are added to create the perfect workable clay that we buy at the pottery supply house.
working with clay:
clay artists over the centuries have invented many ways to shape things out of clay.
Pinch: Use your fingers to pinch and poke a single piece of clay into any shape.
Slab: Roll clay into flat sheets (like a pie crust) to cut and assemble.
Coil: Roll out long clay snakes and twist them into spirals and shapes.
Wheel: Spin clay on a potter’s wheel to form pots and vases.
some tools to use when working with clay:
- your fingers
- rollers and canvas
- Ice cream sticks and toothpicks
- cookie cutters
- plastic bags
- a clay cutter (wire)
- various carving tools, nuts and bolts, old toothbrushes, and anything else I can get my hands on to create texture in the clay
Brother-in-law: This is what you do to get all the air bubbles out of your clay. basically you roll the clay on a flat surface “pushing” and “pulling” the clay to get all the air out. clay straight out of the box is already embedded… you don’t have to worry about air bubbles with new clay.
Kiln: This is a large, hot kiln used to fire clay. you need to fire your clay in a kiln to make it permanent. An oven can reach temperatures of 2500 degrees F. and higher. your home oven may reach 500 degrees f.
clay: is the type of clay that is usually used in schools. It comes in white or red and is fired at a temperature of approximately 1000 degrees C. or 1830 degrees f.
Slip: This is liquid clay… clay with a lot of water added to it. it is used in ceramics (poured into molds). it is also sometimes used as a kind of glue to join pieces of clay together. you need to use slip to “hold” the clay pieces so they don’t fall apart in the kiln. You see, clay shrinks as it dries, so if you haven’t made sure your clay pieces are firmly attached, they will separate in the kiln. it is not enough to simply “stack” one piece of clay on top of the next. use diluted clay as glue.
hard as leather: this is what we call clay that has dried for a few hours. it should feel slightly cool to the touch. leather-hard clay is not dry enough to be fired in a kiln…if a piece of clay is placed in the kiln while it is still wet, it could explode. when the water gets hot… it boils right? well, your ceramic piece will literally “explode” if it contains boiling water or moisture when heated in the kiln.
greenware: When the clay has dried and is ready to be fired in a kiln, it is called greenware. typically the clay should air dry for about a week depending on the thickness of the piece.
bisque: this is the first firing. the clay is usually fired in a kiln twice. once at a lower temperature (the bisque firing). After a piece is bisquetted, it can be glazed, painted or left as is. if the clay is glazed, then it goes into the kiln for a second firing.
glaze: used to decorate clays that contain liquid. it is essentially “liquid glass” or glass particles (mixed with colors or pigments) that have been ground up. the glaze is melted at a high temperature and becomes the coatings seen on a finished ceramic piece.
Cone: The temperature a kiln is set to depends on the type of clay you are firing. Part of the clay is known as cone 4 while part of the clay is known as cone 6. These are simply temperature indicators. a cone, designed to melt at a certain temperature, is used to measure temperature. Earthenware is usually fired at cone 06 – about 1000 degrees C. or 1832 degrees f. your oven is only about 500 degrees f.
Don’t let the clay go down your drain! If clay gets into your sink, you’re in big trouble. always rinse your hands in a bucket of water…the clay will settle to the bottom and you can pour the water out the top (outside) and use the suspended clay at a later time.
© andrea mulder-slater, kinderart.com. this information may not be copied without permission.