SP375 – Lowfire Xtra White Slip

MIXING PROCEDURE Measure the minimum amount of water into the mixing container. Measure the minimum amount of Sodium silicate and an equal amount of water in a separate container. Add the barium carbonate and the soda ash to the water in the mixing container and mix for 5 minutes. Slowly add the clay to the water in the mixing container(while mixing). stop adding clay when it thickens. when it thickens add small amounts of the sodium silicate water mixture until the slip thins. Repeat the process until all of the clay has been added to your mixing container. Allow the batch to mix for the recommended time: Batch Size 50# 100# 300# 1000# 2000# Mixing Time 1 hours 2 hours 3 hours 4 hours 5 hours6) test the slip using the hydrometer and weighing tests to see if any final adjustments are needed. The hydrometer: Used to measure specific gravity of the slip. Hydrometer should be clean and dry. Stop mixing the slip. Place the hydrometer in the slip. The correct reading on the hydrometer is between 1.790 and 1.840. If the reading is below 1.790 there is too much water and more clay should be added to the batch. If the hydrometer white reads over 1.840 more water is needed. The weighing test: Weigh one pint of the slip. A pint of slip should weigh between 820 grams and 828 grams. (28.9oz to 29. 2oz). (be sure to add in the weight of your container). If the slip weighs more than 828 grams more sodium silicate is needed. If it weighs less than 820 grams then more water and clay should be added: to your batch. If adjustments were made to your batch be sure to do a weighing and hydrometer test again.(If adding extra clay was needed do the tests after your batch has mixed for the full recommended time. If extra water or sodium silicate was added then only mix again for 10-15 minutes Overly-Thin Slip This can happen when there is too much sodium silicate and can be corrected by the addition of Epsom salt. Too much water also causes thinness and lowers the specific gravity to a point where poor casting occurs. The addition of more clay and talc in the proportions expressed in the formula will overcome this. Additions of scrap from previous castings also will help. An increase in the percentage of clay at the expense of talc also will thicken the slip. Usually only one of these steps is needed to thicken the slip. Overly-Thick Slip If the slip is too thick or viscous, a little more sodium silicate will thin it to the proper condition for casting. Thickness also can result from too much sodium silicate, and the slip can be thinned with Epsom salt. A slip with too much sodium silicate will move easily around the sides of the container as it is mixed. Slip that are short of sodium silicate will tend to hang up or gel, adhering to the surface of the container while mixing. More water also will thin the slip, but the specific gravity will be lowered. Sometimes it is necessary to add more barium carbonate to counteract the thickening tendency of sulphate, which is associated with talc, water and plaster molds.Thinner slip and also less gelling can be obtained by reducing the percentage of clay while increasing the percentage of the talc a like amount. However, a lower percentage of clay will result in the loss of some workability and plasticity. Usually only one of these steps is needed to thin the slip. Dry ingredients should be measured by weight, and liquid by volume. Either a postage or a gram scale will do for dry materials. After ingredients have been mixed, the scale and pint jars are used to weigh a pint of slip. This simple measure- ment, along with the Hydrometer reading, quickly indicates if the batch has enough water and clay and if it has been correctly deflocculated. Formulas The information we give here is based on average climate and water conditions, factors which can be very stable in some areas and extremely variable in others.(50# dry will yield 5 gallons mixed slip) 50 lbsDry ClayBarium Carbonate* Soda Ash** Water Sodium Silicate50 lbs.0235 oz (6.8 grams)0.47 oz (13.6 grams)2 ½ to 2 ¾ Gal1.6 to 2.6 fl oz.100 lbsDry ClayBarium Carbonate* Soda Ash** Water Sodium Silicate100 lbs.5 oz (13.60 grams)1 oz (27.20 grams)5 ½ to 5 ¾ Gal3 to 5.5 fl oz.300 lbsDry ClayBarium Carbonate* Soda Ash** Water Sodium Silicate300 lbs1 ½ oz (41 grams)3 oz (82 grams)16 ½ to 16 ¾ Gal9 to 14 fl oz1000 lbsDry ClayBarium Carbonate* Soda Ash** Water Sodium Silicate1000 lbs4.8 oz (136 grams)9.6 oz (272 grams)55 to 55 Gal34 to 44 fl oz.2000 lbsDry ClayBarium Carbonate* Soda Ash** Water Sodium Silicate2000 lbs9.6 oz (273 grams)19.2 oz (544 grams)110 to 111 Gal74 to 84 fl oz.*For measuring Barium Carbonate and Soda Ash, it is best to use a sensitive, but inexpensive gram scale. This is espe- ally true for batches under 300 lbs. **The most important thing in making slip is the amount of Sodium Silicate needed to deflocculate the clay body, and that figure varies greatly from place to place. Alternative Slip Mixing Instructions Best results have been obtained by using the following Procedure: 1. Place the water in the mixer, add the barium carbonate to the water and mix for at least 15 minutes (longer if possible). Then add the soda ash and repeat the mixing time. Whiting or calcium carbonate should be added to the water at this point. 2. Add all but 10% of the sodium silicate and mix until it is dispersed. 3. Add the talc and mix for 40 to 50 minutes. With a high-speed mixer a shorter time is required. 4. After thoroughly mixing the talc, continue mixing and gradually add the clay. Mixing should continue until lumps dis- appear and the slip is smooth. As the clay is being added, it may be necessary to add a portion of the 10% of sodium sili- cate, which was retained. Add only enough to keep the slip fluid and mixing well. 5. When the slip has mixed long enough to exhibit smoothness, adjust to the desired specific gravity by adding water." We found a specific gravity of 1.78 most suitable; others will prefer working with a lower one. The addition of whiting or calcium carbonate reduces gel- ling, which sometimes results from additives in municipal water or soluble ions in well water. 6. After the specific gravity has been set, the viscosity can be ad- justed by using a portion of the sodium silicate that had been held out. This can be done by adding a small amount of sodium silicate while mixing and then testing a sample of slip with a viscosimeter. It is always a good idea to screen the slip through at least a 60-mesh screen to remove any trash that may have fallen into the mixer. Better results can be obtained from any slip by using a finer screen, such as 100- or 120- mesh. 7. When the desired viscosity has been achieved, the slip should be ready to cast. However, if the slip is allowed to stand overnight, casting properties will be improved, but the viscosity may have to be adjusted.

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Between 4-6 gallons depending on the clay