Slipmaking

Slipmaking 101 or how to make low fire ceramic slip.

INSTRUCTIONS FOR MAKING YOUR OWN SLIP

50 GALLON RECIPE

Soda Ash and Sodium Silicate are DEFLOCCULANTS. They make the particles of clay all repulse each other (like two north poles on a magnet). Proper deflocculation allows the use of less water to make the slip a liquid, this keeps the molds from getting too wet.

CLAY: The Starcast and Kaolin are clays, they are the actual clay in the formula.

This is for a ceramic slip, compatible with all Duncan, Amaco & Mayco low fire glazes. Bisque is cone 04, Most glaze fire to cone 06.

We sell it premixed in 1 gallon bottle, ups shipment only.

White Slip Recipe (cone 04)

The first time you make slip it all seems mysterious; it is especially important that you measure carefully and keep a written record of what you have done. There are seasonal variations in the ingredients; so, it is important to know what you have done in the past and be consistent. First figure out how many gallons your slip mixer will hold. It is easiest to make 25 or 50 gallons as you will not have to weigh the slip components. Test slip with a hydrometer, or scale, it should read 1.75, and weigh 14.5 lb. per gallon.

1.  WATER ----- 27 GALLONS the warmer the better.

2.  SODA ASH -----4 OZ. DRY

3.  Dissolve Soda in hot water and add to water and allow to stir with mixer running add your Clay.

4.  STARCAST Ball Clay----- 250 LBS. 5 BAGS

5.  Calcium Carbonate (whiting) ----- 50 LBS. 1 Bag.

                       When the mix seems too thick start adding the Sodium Silicate a little at a time

6.  SODIUM SILICATE --12 to 20 OZ. LIQUID

7. Hydrated Magnesium Silicate ----- 200 Lb.

    Let the mixture mix for as long as possible and then rest overnight.

 RED SLIP RECIPE

   1.   WATER ----- 27 GALLONS the warmer the better.

2.  SODA ASH -----4 OZ. DRY

3.  BARIUM CARBONATE ____4 Oz. Dry

         Dissolve Soda and Barium in hot water and add to water and allow to stir with mixer running add your Clay.

4.  REDART CLAY  --- 400 LBS. 8 BAGS

5.  SODIUM SILICATE --12 to 32 OZ. LIQUID

When the mix seems too thick start adding the Sodium Silicate a little at a time

6.  Hydrated Magnesium Silicate ----- 100 LBS. 2 BAGS add the Dolomite with the mixer running. If it clogs up at the top, Turn the mixer off and use a stick to help mix it in.

7.  Let the mixture mix for as long as possible and then rest overnight.

WHAT THE COMPONENTS DO:

• Barium prevents white scumming on the bisque.
• Hydrated Magnesium Silicate functions to prevent the glazes from crazing and to make the bisque white. 

 There are two properties of slip that we want to test frequently. They are specific gravity and viscosity. Specific gravity means how much more than water does the slip weigh. For instance: A gallon of water at 70 degrees weighs 8.3 lb. Lets say we weight out a gallon of slip and it weighs 14.4 lb. Simply divide 14.4/8.3= 1.73.This is a ratio, it is generally accepted that 1.75 is good for slip casting. So our slip is a little light at 14.4 lb. per gallon, water weighs less than clay so we have too much water in our slip, we can’t take it out so we have to add more dry materials. (if the slip was too heavy we could have added water.) Okay, now we weigh the slip again and it is 14.5 pounds plus a little. Do the math and you can tell that you are right at 1.75.

 Unfortunately 1/10 of a pound is not as accurate as we would like so we use grams (1/10 lb. = 45.4 grams)

            The Viscosity refers to how thick a liquid is. With slip we like to change how thick it is by adding more deflocculant (Sodium Silicate) NOT by adding water.

            How thin do you want the slip to be? It depends on what you are making.  Hollow beads or tiny miniatures require thin slip, large items require thicker slip.

Measure viscosity by how long it takes (in seconds) to drain out of a container with a small exit hole. The best thing to do is find some slip you like, then time it using a viscosity meter how long it takes until the flow changes from constant to drips..

Each time you do this test try to do it exactly the same way.

If the slip is too thick and the specific gravity is right, then you can add some deflocculant, or some special slip thinner. These are very powerful in their action add only 2-3 drops per gallon.

           Other Qualities.

• Absorption: How porous the bisque is determines how easy the glaze is to apply, it changes by what cone the slip is fired to, and the composition of the slip.
• Thermal expansion: Determines glaze fit, a too tight fit and the glaze falls off (shivering ), too loose and the glaze crackles (crazing). Glaze fit is determined by the amount of talc in the slip and the bisque temp.
• Shrinkage: Is complicated to control, but it is useful to know so that you know how to size the molds, more water in the slip gives increased shrinkage and increases cracking in the mold.
• Over deflocculation: Slip casts slow, inside of cast appears sharp and greenware is brittle, hard. Noses and other high points may turn brown when dry.
• Under Deflocculation: Slip casts fast, seems soft and flabby, molds get wet sooner. inside of casts look smooth.

this from Duncan 1982......

SUGGESTED METHOD OF PREPARING CASTING SLIP 

The first requirement for making a good casting slip is the realization that it cannot be done by any hard-and-fast rule. Many factors enter into the making of a good slip, any one of which will change its quality and working properties. The main factor is the purity of the water, but many other factors will have their effect. 

CARE AND ACCURACY WILL PAY GOOD DIVIDENDS 

1. For each 100-pound batch of clay, pour five (5) gallons of clean water into the mixing barrel or container.

2. Draw off one (1) pint of this water into a separate container and add one ( 1) 01;1nce dry soda ash to it. Mix thoroughly.

3. To the soda ash-water mixture, add one-quarter (1/4) cup of sodium silicate ('N' Brand) and mix well. (Other brands may vary in performance.)

4. Pour the mixture into the mixing barrel.

5. Gradually add 100 pounds of dry clay to the water mixture, stirring constantly to allow proper dispersion. If mixture becomes too thick to be stirred easily, an additional 1/4 cup of sodium silicate can be added A FEW DROPS AT A TIME. Resume adding remainder of dry clay, mixing thoroughly to prevent lumps of undissolved clay powder.

6. Draw off exactly one quart (32 fl. oz.) and weigh on a scale. (A diet scale which shows ounces and grams is excellent for this purpose.) This quart should weigh approximately 56 oz. net. If it is heavier than 56 oz. net, add small amounts of water to the entire clay mixture and draw off a new sample for weighing. Repeat if necessary. If the quart weight is between 50 and 56 oz., allow some of the water to evaporate to increase the weight. If the weight is less than 50 oz., solids can be added back, however, this is very difficult and tricky to control. Care and accuracy in mixing is the best assurance of proper slip.

7.     Allow the slip mixture to set overnight before using, to permit proper aging.

8.     As a safety factor, strain slip as it is poured into containers which will be used for casting. This will remove any foreign materials which may have fallen into the mixing barrel as well as catching any small lumps of clay.

ANALYZING SLIP DEFECTS

1.  Short, crumbly or brittle greenware -caused by too much sodium silicate in the slip mixture.

2. High shrinkage or cracking in mold -too much water in the slip.

3.      Gummy ware after the normal set-up time-too much soda ash or too little sodium silicate in the slip.

4.      Clay settles to the bottom of slip container, leaving a large waterhead; (sometimes floating black particles are visible on the surface) -can be caused either by too much sodium silicate and/or too much water in the slip. 

5.      Thick slip after normal aging period -high evaporation of water.

slip calculator