This is how much casting slip 10,000 grams of powder makes

There are 8.8 liters of slip in this 2 imperial gallon bucket. The cone 10 stoneware slurry was propeller mixed in a larger bucket. First I stirred about 3/4 of the projected 44g of Darvan into 4000g of water. Then I dumped in 10,000g of the powder (shaken in a plastic bag) and let it sit to slake as much as possible. Then I used a high-energy propeller mixer, and to finish, trickling in extra Darvan until the rheology was right. The slip itself thus weighs 14 kg (31 lb) and has a specific gravity of ~1.75. It has sat overnight and formed a film on the top, but has not settled (indicating that it likely is not over deflocculated). The casting process enables even a hobbyist to make his own custom recipes and tune them over time. Would you like to develop a recipe? An account at Insight-live.com is the first step, that’s where you’ll keep all the development notes, pictures and data.

Related Pictures

Glazes Are Crazing on This Casting Porcelain

The casting process enables a unique and effective fix

Generated with a prompt for a crazed glaze on a slip cast mug

This picture has its own page with more detail, click here to see it.

This potter almost has the casting process working, making these beautiful porcelain mugs. They are fired at cone 6 using a transparent glaze over underglaze decoration. But the devil is in the details. Look closer to see it: Crazing. Why? The reason is evident on the SDS for the body. Notice it has 10.5-15.8% crystalline quartz (or silica). This is not enough to prevent crazing in typical glazes. L

Almost always, the solution is to find or formulate a clear glaze having a lower thermal expansion (in this case, a lot lower). But with casting bodies we have another option: Mix our own. Unlike glazes, porcelain recipes are typically just three materials: kaolin, feldspar and silica. The starting percentages are simple for cone 6: 30% feldspar to vitrify. And 25% silica to fit the glaze. That leaves 45% kaolin. It is that easy! Of course, you need to choose which feldspar and kaolin. Start with the L3778G recipe. Its information page (the preceding link) is also a launching pad having dozens of links, enabling you to dig as deep a desired into understanding casting slips (the materials are cheap so losing a few batches while you learn deflocculation is not a problem).

Here is how vigorously a deflocculated ceramic slurry should be mixed

A video of the kind of agitation needed from a propeller mixer to get the best properties out of a deflocculated slurry. This is Plainsman Polar Ice mixing in a 5-gallon pail. Although it is quite plastic compared to industrial casting slips, it has a specific gravity of 1.76, is very fluid and casts well in the hands of a potter. These properties are a product of, not just the recipe, but the mixer and its ability to put high energy into the slurry.

I can mix all this powder into that little bit of water to make a casting slip. How?

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This is 8.4L of water (in the bottom of that pail) and a 20kg bag of Polar Ice porcelain casting clay. Amazingly, it is possible to get all that powder into that little bit of water and still have a very fluid slurry for casting. The volume will increase to only 2/3 of this 5-gallon pail. How is this possible? That water has 100 grams of Darvan 7 deflocculant in it, it causes the clay particles to repel each other such that I can make a liquid with only a little more water than is in a throwing clay! All it takes is a few minutes under a good power propeller mixer.

Videos

Links

Glossary	Slip Casting A method of forming ceramics. A deflocculated (low water content) slurry is poured into absorbent plaster molds. As it sits in the mold, usually 10+ minutes, a layer builds against the mold walls. When thick enough the mold is drained.
Glossary	Deflocculation Deflocculation is the magic behind the ceramic casting process, it enables slurries having impossibly low water contents and ware having amazingly low drying shrinkage

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