CERAMICS: BACK TO BASICS An Introduction to all things clay

What is Clay?  Decomposed rock called Granite  Made of a combination of 3 things:  Silica ○ Sand is made of silica ○ When heated becomes glass  Alumina ○ A kind of flux ○ Lowers the melting point of the silica and clay  Water ○ Physical water- makes clay moldable ○ Atmospheric water- water present in the air

Describing Clay  Plasticity  Describes how easily clay can be molded and hold its shape  Clay Body  Clay mixed with other ingredients to change the properties of the clay. ○ Properties include: color, firing temperature, degree of plasticity.  Water management  Need to control the amount of physical water in the clay. ○ In general: less water = the less plastic (less moldable)

The 6 Steps for Water Management Lots of Water Water and Clay Water is gone- only Clay left

Water Management- Steps 1-2  Slip  Watery clay; at least equal parts of clay and water  Used to help weld pieces of clay together  Moldable Clay  Just enough water so the clay can easily be molded and shaped  Still has lots of water that can evaporate

Water Management- Steps 3-4  Leather Hard  Still moldable but feels hard.  Will break if not careful  Bone Dry  Green-ware  Looks totally dry  Only has atmospheric water in the clay

Water Management- Step 5  Bisque  first firing ~1600 F  Gets rid of most of the atmospheric water (started to chemically change the Clay-can’t put water back into clay)  Makes the clay harder and shrinks some  Makes it easier to glaze

Water Management- Step 6  Ceramic  Final firing-Glaze firing  Clay is Vitrified- permantly hardened  Chemically pulled water out of the remaining clay  Parametric Cone is a type of measuring system for ceramics  Temperatures for final firings ○ High Fire clays ~2300 F Cone 10 ○ Mid Fire clays ~2100 F Cone 6 ○ Low Fire clays and Bisque ~ 1800 F Cone 04

Firing Clay  Why do you need to fire clay?  Makes clay less porous so it can hold water.  What happens when clay is fired?  Removes all of the atmospheric water  Fuses the Alumina and Silica together  Cannot become plastic anymore  Where does clay get fired?  Usually in a kiln which is a kind of oven  Can also fire ceramics in a pit or open fire

Glazing  What are the differences between Glaze and Clay?  Glaze has more Silica and Flux  Glazes also have more minerals and impurities to give it color.  What purposes do glazes serve?  Makes piece water-tight  Sanitary-easier to clean  Decorative

Applying Glaze to a Piece  Step 1- clean off piece  Step2- mix up the glaze- all sediments need to be mixed well  Step 3- Apply glaze (thickness of a credit card)  Dip- submerge and count to 2 seconds  Paint- two thick, even coats  Step 4- wipe off the foot of your piece  anywhere clay will touch the kiln shelf cannot have any gaze because it will melt to the shelf!