Slip-casting a simple cylinder
This project follows on from our two-part cylinder mould but the principle for slip-casting is the same whatever mould you use.
This is a quick way of making items where they all need to be exactly the same, but this doesn’t mean that the process is limiting, because there are still many things you can do to change the look of the item once it’s been cast, if you want to.
Casting isn’t for everyone, but it is something you should at least try, to see what potential it holds for experimentation and bulk making.
You will need:
• A mould eg, this simple cylinder
• Casting slip: earthenware, stoneware or porcelain – available from your clay supplier readymade for use. 12.5l makes about 20 casts, each needing about a pint to fill the mould. The number of casts depends on the type of clay and size of mould. Porcelain is cast thinner, resulting in more items.
• A wooden spoon or spatula for stirring
• A sieve (the kitchen variety is the easiest to use in this instance)
• Plastic jugs
• A natural sponge
• Wet and dry sandpaper
• A chamois leather, stretched and fixed over a board
Stir the casting slip thoroughly using a wooden spoon. It will be quite thick to begin with, but will become more fluid as you stir. It’s ready when it looks lump-free and runs very freely from the spoon. The longer you mix, the better.
Decant a jug-full of slip from the container then pour it through your sieve into a second jug. (You could pour the slip through the sieve directly into the mould, but this is fraught with potential spillage problems – it’s best to avoid accidents at this stage!).
Pour the slip into the mould, filling it right to the top in one go, as shown.
Time your casting slip according to type of slip used: A kitchen timer is a good tool for this job.
White earthenware: 20 – 30 minutes. Firing temp 1000°C to 1150ºC (1832°F to 2102ºF)
Red earthenware: 20 – 30 minutes. Firing temp 1000°C to 1150ºC (1832°F to 2102ºF)
Stoneware: 45 mins – 1 hour. Firing temp 1160°C to 1290ºC (2120°F to 2354ºF)
Semi-porcelain/ high-firing white earthenware: 20 – 30 minutes. Firing temp 1100°C to 1260ºC (2012°F -2300°F)
Porcelain: 5 – 10 minutes. Firing temp 1260°C to 1280ºC (2300°F to 2336ºF)
Bone china could be added to this list, but it’s not a slip to choose when first starting to experiment with slip casting, because it requires special firing treatments and is notoriously difficult to handle. If you have no prior experience of casting, start with white earthenware because it’s easy to cast and fire, and is the cheapest option.
Top the slip up periodically as you need to maintain the level to the rim. You’ll see it begin to shrink from the edges as the plaster draws the water out of the slip.
Pour the slip out of the mould and back into the bucket when the correct casting time has been reached. Hold it over the bucket for a while, then transfer it to two battens suspended over a bowl to allow the remainder of the slip to flow out.
The cast’s ready to remove from the mould when the surface of the slip no longer looks shiny and isn’t tacky to the touch. The clay will also have shrunk away from the plaster walls considerably by this point.
Using a plastic kidney, remove the excess slip from the top of the mould.
Cut away the ‘spare’ carefully, holding your knife in a vertical position and making sure none of the waste clay falls inside the form.
Lie the mould on its side and remove the restraining straps. Lift off one half of the mould, then elevate the second half and allow the cast to gently fall out into your hand. It should be firm enough to handle without damaging the surface in any way.
Place the cast on a board and allow it to dry out completely.
Once the cast is bone dry, sand off the seams and base with wet and dry sandpaper until the surface is smooth and the seams no longer visible.
Dampen the surface of the chamois leather-covered board then sit the cylinder base on the surface and rotate it in a circular motion until the underside is smooth and flat.
Repeat the exercise for the rim, but be slightly gentler because the rim is more vulnerable to breaking.
This is the best method for levelling.
Sponge over the seams with a damp sponge (the water won’t affect the surface unless you really saturate it, in which case simply allow it to dry out again before continuing.)
To refine the rim, dampen the clay by wiping it around with a sponge then carefully cut away any excess clay on the inside with a sharp knife. Once all has been removed, smooth over the rim again with the sponge to neaten and smooth it off.
The cylinder is now finished. Allow it dry out completely before bisque firing.