Ceramic bowls made from slip.
The process of turning clay into casting slip is simple but a little bit time consuming. There are many online resources that can give you further tips if you would like to make your own casting slip, but this is the basic technique.
Save your left over clay in a bucket and let it dry. When the bucket is 2/3 full of bone dry clay, add water until it’s a few inches below the rim. Allow the clay to slake for 24 hours and then mix the slurry by hand with a stick. Once the slip is roughly mixed up, you can use a drill with a paint mixer attachment to mix it into a smooth slurry with the consistency of thick cream. Keep mixing until any lumps are dissolved.
The weight of 100 ml of water is 100g, but now that clay is added, you will need to determine the specific gravity of your slip to see if it is strong enough to use for casting. First weigh your container so that you can zero out its weight. Then fill it with 100ml of slip and weigh it. If you get between 175-190 g, you are ok – 180-185 is a good medium to aim for. It is good to make a note of the weight of your slip so that you find a slip that works for you. If it is too heavy, add water – if it is too thin then leave it to stand for a few hours and then pour away the water at the top.
Now add a few drops of a deflocculant such as sodium silicate to the slip to make it more fluid and easier to pour. It is important not to add too much because that will cause slow uneven drying and soft spots in the finished piece. Mix the deflocculent into the slip with your trusty drill and see how the slip pours. If it isn’t fluid enough for your taste, then add a few drops more…
The beauty of making your own casting slip is that your slip will be compatible with the clay you normally use – so there will be no issues caused by uneven shrinking or cracking when you mix casting and hand building techniques in the same body of work.