DRY SLIPS

 

White Diamond

White Diamond is a quality casting slip designed for whiteness and fast castability.  White Diamond is formulated for the hobbist as well as production ceramics.

 

 

Recommended, bisque

Cone 04

Recommended, glaze

Cone 05-06

Dry Shrink

3.2%

Fired Shrink

5.6% at Cone 04

Absorbtion

16% at Cone 04

 

Stoneware 18B

A stoneware casting clay formulated with IMCO’s western ball clays. Stoneware 18B has easy mixing and excellent casting  properties.  Stoneware 18B fires to a cream color in oxidation and gray in reduction.  

 

 

Recommnded

Cone 8-10

Dry Shink

4%

Fired Shrink

13.5% at Cone 10

Absorption

2% at Cone 10

 

THE SCIENCE OF SLIPMAKING

 

Making good slip requires attention to detail and the right equipment and materials.  Many factors can affect the quality of your slip such as changes in temperature, humidity and the chlorine and chemicals which are added to water supplies. Accurate measurements of viscosity and specific gravity are also important.  Also, for best results, make your slip 24 hours before using it for casting.  Adjustments may be necessary to fit your climate, water and general studio or plant conditions.   ALWAYS MEASURE DRY INGREDIENTS BY WEIGHT, AND MEASURE SODIUM SILICATE AND DARVAN IN LIQUID OUNCES.

 

SUGGESTED EQUIPMENT FOR SLIPMAKING

                                

Slip Mixer                   With a motor and blades which are capable of properly mixing your batch of slip.

Gram Scale                 A triple beam or electronic balance.

Viscometer                  Developed to measure the viscosity of slip, which indicates the amount of slip that flows per second.

Liquid Ounce Measure  Sodium Silicate for instance, must be measured by the liquid ounce. Four (4) ounces of measured Sodium Silicate, for example, weighs approximately 5 ounces on a scale.

Respirator                  (OSHA Approved)

Sieve                          A sieve is an invaluable aid in screening your slip.

 

SUGGESTED CHEMICALS FOR SLIPMAKING

 

SODIUM SILICATE - Soda and silica combined in approximately equal parts. It is soluble in water and is used as a clay deflocculant in casting slips. Sodium silicate is usually bought as a concentrated solution. It is in this form that  it is introduced into casting slips. Never add pre-measured sodium silicate to the batch all at the same time. Add only in small amounts.  Sodium Silicate may be stored for extended periods in tightly closed plastic containers. (Aluminum, galvanized iron or zinc containers SHOULD NOT be used.)

 

SODA ASH  - Soda Ash works with Sodium Silicate to aid in deflocculating.  The correct combination of the two will give proper casting qualities.  Soda Ash works to dissolve lignite in clay.  It works as a deflocculant, but if only Soda Ash is used as a deflocculant your clay will become sticky.  If Soda Ash is not stored in tightly closed containers, a chemical change occurs and it becomes Sodium Bicarbonate (Baking Soda).  If this occurs it will then act as a flocculent (it will thicken) instead of as a deflocculant.

 

BARIUM CARBONATE - It is sometimes necessary to use Barium Carbonate in your slip batches to neutralize sulfates that may be present in the clay or in the water and sulfates leeched from molds used in casting.  If your application requires the use of Barium Carbonate, use caution because Barium Carbonate is poisonous in its raw form.

 

DARVAN - Darvan is an organic deflocculant, which can be used with less fear of over-deflocculating.  It is especially effective in hard water areas.

 

                                                  IMCO SLIP                                                

 

100 pounds of slip

5.65 Gallons of water by volume

1 ounce of Soda Ash by weight.

4 ounces of Sodium Silicate by volume.

 

 

After clay is thoroughly mixed, age

over night and test.

 

 

MIXING PROCEDURES

 


1.                 Wearing a respirator is highly recommended prior to starting slip mixing activities.

2.                 Measure water carefully and pour water indicated for your size batch into the slip tank. Start mixer.

3.                 Accurately measure the minimum amount of Sodium Silicate indicated for your batch.  Add to water and mix for 5 minutes.

4.                 Measure the amounts of Soda Ash and Barium Carbonate, if needed, indicated for your size batch and add to one quart of warm water.

5.                 Add diluted Soda Ash and Barium Carbonate to the water which is in the tank.  Mix for 5 minutes.

6.                 While the tank is still mixing, slowly add 1/3 of the clay indicated for your size batch to the water.


 

1.                 After mixing a short time, allowing the Sodium Silicate to thin the batch, add 1/3 more of the clay.  Allow clay to mix into the batch.

2.                 After mixing a short time (approximately 10 minutes), add the final 1/3 of your clay to the mixer.


 

1.                 The mixing time should be approximately as follows:  100 lbs -  2 Hours; 300 lbs -  3 Hours;  1000 lbs - 4  Hours;  2000 lbs - 5 Hours.

 

Until the slip is thoroughly tested, one should refrain from judging the usability of a slip by observing it only. However, we do not recommend that any adjustments be made to the formula until 24 hours after batch is made and tests are repeated.

 

 

 

 

 


SPECIFIC GRAVITY

A balance and a bottle with a narrow neck are all that are required to determine specific gravity.  Measuring specific gravity requires only that you fill the bottle to the very top with slip, wipe off any spillage and weigh it, then  repeat using water.  Apply this simple formula to obtain the specific gravity:                           A  - B

                                                                             C - B  

“A” equals the weight of the bottle filled with slip, “B” the weight of the bottle  and “C” the weight of the bottle filled with water.  Specific gravity of IMCO slips should be between 1.76 and 1.80.

 

 

 


MAKING A VISCOMETER

 

Materials needed:        6" length of 2" pvc pipe

                                 Cap for the pipe

                                 9/64" drill bit

 

Take the 6" length of pvc pipe and glue the cap to one end of the pipe.  Drill a 9/64" hole in the center of the cap.

 

 

 


USING THE VISCOMETER FOR THE VISCOSITY TEST

 


 

1.                 Measure 8 fluid ounces of slip.

2.         Prepare a measuring cup or graduated cylinder that will measure at least 4 ounces.


 

I.                   Place a finger over the hole in the viscometer.

II.                Pour the 8 ounces of slip into the viscometer.

III.             Remove finger from hole and start timing simultaneously.

IV.              Determine the time required for four ounces of slip to flow from the viscometer.  Normal slip should take 30 to 40 seconds.

 

It  is recommended that slip be screened through a 60-mesh sieve before using. REPEAT TESTING AFTER 24 HOURS.  MIX BATCH FOR 30 MINUTES THEN BEGIN RETESTING.

 

ADJUSTING THE BATCH   -        Viscosity too high, specific gravity too high - Add water.

                                      -        Viscosity too high, specific gravity normal - Add Sodium Silicate

                                      -        Viscosity too low - Add clay

 

If extra clay is added, mix the batch for the full recommended time (i.e., 3 hours for a 300 lb. batch).  On the other hand, your slip need only be mixed for fifteen minutes if only extra water or Sodium Silicate is added.  If your weight and viscosity readings are slightly higher or lower than the ranges given in our Testing Procedures, casting under your conditions will be the ultimate test.

If your weights and Specific Gravity are not within recommended limits, but your slip casts well, you should not make any adjustments.

 

CAUTION: Adding too much water to your batch may make your slip easier to drain, but can  cause cracking in your molds and can produce brittle castings.  Lignite may also surface.

 

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