If you have never worked with clay before please take the time to read the information below, it's important that you understand how to safely work with clay at home.
There are 5 rules when working with clay:
1) Use absorbent tools and work on absorbent surfaces so the clay doesn't stick (wooden board & rolling pin, plaster mould etc).
2) When joining clay ensure the pieces have the same moisture content, so that they continue to dry and shrink at the same rate (clay shrinks by up to 30% as it looses it's water content).
3) When joining use scoring and slip; the drier the clay the heavier the scoring and thicker the slip.
3) Do not trap air, hollow areas will need a small hole for air to escape (air expands when heated and would cause explosions in the kiln if trapped).
4) Decorating slip is only applied to damp work. Underglaze can be applied to damp, dry or bisque fired work. Glaze is only applied to bisque fired work.
As with all rules these can be broken once you know how, but if you follow them as you start out you shouldn't go too wrong.
You don’t need to store clay anywhere special, room temperature is fine, just keep it wrapped up or in a plastic box and away from direct sunlight.
If you re-use clay you need to be very very careful not to trap air or it will explode in the kiln.
Alternatively you can return to us to recycle, please dry it out first.
CLEANING; HEALTH & SAFETY
Clay-dust is very bad for you, so make sure you clean your work station thoroughly with water.
Don’t wash clay down the sink, you’ll eventually block your pipes. Wash everything into a tub and then throw into a flower bed or flush down the toilet.
Oxides and glazes are toxic to marine life, so wash these in a jar and when it's settled out after 3days you can pour off the water and scoop the sludge into the bin.
Clay contains 20-30% water, so as it dries it shrinks by up to 30%. Shrinkage is the main thing you need to control in pottery, ensuring that pieces joined together dry and shrink at the same rate, otherwise you'll get cracks.
To achieve this it helps to ensure work is roughly the same thickness all over (if this isn't possible you can wrap thinner areas in plastic as the piece dries, to even out drying). When you join parts together they need to have the same water content.
If you are worried about any of this ensure your work drys slowly by wrapping it loosely in plastic.
Clay Firing Temperatures
Earthenware: Low-fired ware (under 1050) usually still porous after firing—must be sealed with a glaze to be functional.
Stoneware: Vitreous ware fired at 1050 to 1326 degrees celsius, literally as hard and durable as stone. We fire to 1240.
Vitreous: transformed into a solid state impermeable by water (our clay is stoneware so is vitreous after firing).
Porcelain: High-fired vitreous clay containing kaolin, silica, fluxes, and often ball clay to increase plasticity, with total clay component not more than 50%. Usually pure white in color; some porcelains may fire translucent where thin.
Grog: is added to clay to reduce shrinkage and give structure for throwing or handbuilding. Our standard clays standard contains 10% fine grog.
The building, decorating and firing process
Pottery goes through at least two firings and needs to be completely dry before it goes in the first firing, so please give your work to us for firing when it's as dry as possible.
Bisque firing is the first low-temperature firing, during which clay becomes solid without vitrifying, so it is still porous and can take glaze. The second firing (where glaze is usualy applied) takes the clay to full maturation temperature, which in our case is 1240 celsius.
Coloured slips are made from clay, pigments and water and are added before bisque firing, when the clay is still damp.
Underglazes can be applied either to greenware (unfired) or bisque fired ware.
Glaze is applied to bisque fired ware and you can either purchase painting glazes fro us to apply yourself or pay for work to be dipped. Glazes have a high proportion of melting ingredients (fluxs and silica) so they behave more like glass than clay.
Clay in different states
Green: clay in any state before bisque firing. As a general rule slips can only be applied to green ware, glazes can only be applied to bisque fired ware (these rules like any can be broken, but only if you understand the results).
Slip: clay in a liquid state. Decorating slip contains coloured oxides
Underglaze is slip coloured with brighter pigments and contains a melting agent so that it can be used on bisque.
Plastic: wet and pliable (straight out of the bag)
Leather hard: when the clay has lost much of it's moisture and is, well, leather hard :-) like a hard cheese and the ideal stage for adding decorating slips.
Bone dry: when the clay has lost all of it's moisture, it is at this stage it can be bisque fired and it's too late to add decorating slips.