How to Make a Slip for Ceramic Molds

Ceramic slip is also used to bind pieces of clay together, such as handles.

Making your own slip for slip casting provides a cheap alternative to purchasing it yourself. Besides, you can find clay in stores more easily than you can find slip. Making slip is a careful balance of chemistry. According to "Ceramics Made Easy," slip should ideally weigh just over 14 1/2 pounds per gallon, so if your end result weighs more or less than this, you will want to try again. A better measure is to use the specific gravity measurement, which should ideally equal a ratio of 1.75. However, you will want to use a thinner slip for casting small objects and a thicker slip for casting large objects.

Things You'll Need

• 3 oz. barium carbonate
• 27 gallons warm water
• 4 oz. soda ash
• 100 lbs. clay
• 12 oz. sodium silicate
• Basin
• Thermometer
• Hydrometer
• Stirring stick

Instructions

1. Pour warm water into a basin. Temperature affects the specific gravity of your slip and will skew your measurements. You want the water to be as close to 70 degrees F as you can get it. Bob a thermometer in the water to keep an eye on it and adjust the temperature of the water accordingly as you fill the basin with 27 gallons.

2. Pour 3 oz. of barium carbonate and 4 oz. of soda ash into the water and stir them in with a stirring stick.

3. Pour in your clay. This clay needs to be absolutely dry and in powder form. Any moisture in it will be counted with the water in the basin. Stir as you pour.

4. Pour in your sodium silicate, starting with 12 oz. The sodium silicate and soda ash keep the clay particles from sticking together, ensuring that you have an even mixture. Stir the mixture for half an hour.

5. Scoop some of the mixture into the tube of a hydrometer. Look at the gradations above the tube. They should resemble a thermometer. Look under the specific gravity column. It should be close to 1.75. If it is not, add more clay, or water, or sodium silicate, and keep taking measurements to see how it affects the specific gravity. Stop when it reaches 1.75.

References

• New Mexico Clay: How to Test Your Slip
• Ceramics Made Easy: How to Make Ceramic Slip
• Ceramics: Making Your Own Ceramic Slip