Notes from the first time throwing store bought clay on the home made wheel. The first vessel was attempting to be a bowl but the side began to blow, this was rescued by turning the broken rim into a spout, creating an oil lamp like vessel. 

Things I learnt:

• The bought clay formes vessels much more easily
• Wedging is super important and may simply work better with store bought clay potentially due to the purity and consistency of the particles
• Spin the wheel when cutting vessels off
• Walls blow out of bowls, may need less water, more speed, better posture or different hand movements

Things I need to learn:

• Postures and hand motions/ brace positions for throwing  
• make wood scrapers and spatula forming tools
• need more boards and wedging/drying surfaces

To attempt throwing natural clay I collected sandy clay, plastic clay and a sandy plastic clay from natural deposits from the northern slope of the Windsor bridge (Hawksbury River) at a depth of around 2 meters. The natural clay in this area is a banded orange yellow ball clay and the deposit showed no sign of bioturbation (organic or animal disturbance) which indicates a clean, undisturbed, clay deposit.

Firstly I mixed the three clays in a bucket of water at a ratio of 1:1 and left over night

The slush was filtered through a screen to remove any organic material which there was very little of, and to neatly mix the three clays together. Large clumps of plastic clay would not break down, these I left on the screen to dry.

Warning: I had to protect the drying clay from the chooks, believe it or not, they will eat clay clumps!

The contents of the bucket was allowed to settle over the next week, allowing the excess water to be ladled off the top. This process imitates the natural process of clay setting on a river bed.

Silty sand was collected from the yard and sieved through a piece of hessian to remove rocks and large particles and used as temper (grog). The temper was added to the plastic clay from the sieve frame.

Wedging to work the clay into a single homogenous body between the temper and the plastic components of the naturally sourced clay was successful in creating a clean clay matrix ready for throwing, similar to store bought clay.

I attempted to throw this clay on the pottery wheel and managed to work the clay into a small vessel before oversaturation, this particular make up seems to be slightly too absorbent, there may also be something off kilter with the wheel, will need to practice with store bought clay to further understand the variables between the clay body and the wheel itself.

Reflection:

In hindsight natural clay creates a lot of torque, the features tear them selves apart as the wheel turns. This could be because the particles are too large, temper is poorly mixed or in the wrong ratio. There may also be an issue with the wheel, as this is the first time using the home made wheel.

The slush was further mixed by hand an kept to be used as a slip on future projects, it offers a beautiful yellow pigment.

The remaining natural clay has been put aside until further practice can be undertaken with store bought clay, and this will be revisited in future

Amendment:

There was a issue with the wheel, it was sitting on an unlevel surface, once this was corrected the rate of successful vessels became much higher.

Clay Bodies and Minerals

Several materials are referred to as clay. General properties for the classification of clay may include plasticity, staining of the hands, absorption of water before or after firing, shrinkage or reduction as water is removed and the reaction to heat. Each different clay is composed of different amounts of minerals which determines the characteristics of the resulting pottery. Raw material differs regionally, and mixing clay bodies from different areas is common to create a mixed matrix. 

• Kanolin: Originating in China, used for porcelain production. Also referred to as china clay.
• Ball Clay: Extremely plastic, fine grained sediment clay. Small amounts may be added to Kanolin to increase plasticity.
• Fire Clay: Slightly lower fluxes than kanolin. Increased firing temperature. May be added to other clays for stoneware type bodies.
• Stone Ware Clay: Between fire and ball clay. Fine grain yet fire resistant.
• Common Red Clay/ Shale Clay: The pigment of this clay comes from ferric oxide impurities. good for bricks. Not typically used for clay, except for certain deposits.
• Bentonite: Extremely plastic, can be added to short clay to increase plasticity.

More than one clay body is often the recommendation, for throwing clay must:

• Highly plastic and flexible
• low absorbance
• strong (coarser particles ie fire clay, grog* or temper)
• Ball clay generally meets these stipulations

*Grog or temper is usually clay that has been fired then ground up and added to fresh clay, however the term also extends to anything which adds ‘grit’ or larger particles to the clay body ie sand, or paper in the case of Kanolin. General rule of thumb for grog to clay is 8% – 10% of clay body.

Collecting and Processing

Locate:

• Commercial clay is mined from high grade sources
• Working with machinery allows me to reach similar natural clay bed depths, which is a purer deposit than that on the surface of mud banks
• To test clay composition take a wet sample and roll it into a sausage, bend the roll into a ‘C’. If it stains your fingers and cracks it is silt, if it is buttery and can form a ‘C’ it is clay

Wet Process:

To remove foreign materials, which can cause cracking or explosion due to variants in firing temperature and cavities caused by organics.  

• Mix clay and water in bucket until completely dispersed and thin slurry
• Pour your slurry through a sieve or cloth
• Let sit for a day or two. The clay will settle and allow you to pour off access water
• You can now allow the rest of the water to evaporate off or you can strain the water through a bed sheet or something fine enough to keep the clay out.
• Dry processing is also an option but much less successful 

Temper and Clay Bodies:

• Use sand, crushed shell, or old ceramics to lower the rate of expansion and reduce cracking
• Distribute temper evenly through dried clay, 10% temper = clay volume
• Make clay disks like pancakes and sprinkle temper between the ‘pancake stack’ 
• Kneed and wedge this pancake stack, this is your clay body