How to make Casting Slip

Materials and Supplies Needed

1. Specific Gravity supplies
2. deflocculant

Steps

1. Take the dry clay and add some water to it
2. Measure the specific gravity of your slip SEVERAL times (3 times)
   • It should be between 172-180
3. Once you have measured your specific gravity you need to add deflocculants
   • It is hard to say what viscosity your clay should be at but you can tell if you have added too little or too much by these two characteristics
     • If your casting slip has too much deflocculant you can tell by running your finger through the slip and you should see “skinning” a ridge this is too much deflocculant and difficult to get back as you must add more slip and the specific gravity will be off
     • “Gelling” is when there is too little deflocculant. The characteristics to look for is when you leave your slip for 20 minutes and you run your finger through it and you can see a trail that is called “gelling”
   • If you let your slip sit for half an hour it shouldn’t gel or skin
   • Eventually it will skin and gel you just don’t want it to skin or gel for at least half an hour
4. One more thing you can do once you have the “perfect” casting slip you can use a Ford Cup and measure the amount of time it takes to flow out of the ford cup

Casting Slip Recipes

Below are tested casting slip recipes for high-fire porcelain. Both use Darvan 7 as a deflocculant — always add deflocculant gradually and check specific gravity as you go. Target specific gravity is 1.70–1.75 for most casting applications.

Reeves Porcelain Casting Slip (Cone 7–10)

Adapted from John Reeves’ throwing body. Translucent and prone to slumping — best suited for smaller, more refined forms. Works in both oxidation and reduction atmospheres.

Additions: Water ~35%, Darvan 7 ~0.35% (amounts are approximate — adjust to reach target specific gravity).

Highfire Porcelain Casting Slip (Cone 10)

A reliable cone 10 porcelain casting slip using Grolleg and Nepheline Syenite for translucency and good casting properties.

Mixing instructions (5-gallon bucket):

1. Add 2 gallons of water to your bucket
2. Weigh 68g of Darvan 7 — add two-thirds to the water first
3. Add dry materials one at a time, mixing between each addition
4. Add remaining Darvan if needed to reach target consistency
5. Check specific gravity — target is 1.70
6. Add water in small amounts, mix, and recheck until you reach 1.70
7. Let slip rest for 24 hours before use

Kevin

I am a visually impaired ceramic artist. I have been making for around 8 years now. I specialize in functional colorful pottery. Mainly nerikome and other decorative processes.

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