The worst laminations were at the bottom where wall thickness was the most variable and therefore the most drying stresses occurred. I actually do not know. Obviously, experience gained from using the clay body over many kiln firings and with various glazes will be vital in building confidence in the revised recipe. Its up to you to gather and evaluate the information, to get to know the ma­terial on a practical “nuts and bolts” level. A fine white potassium feldspar used in clays and glazes. Once a small batch of revised clay body tests well, mix up another small batch and fire it in other kilns or even the same kiln. Because of its smaller particle size, copper carbon­ate disperses readily into the fired glaze. Which I'm told is superior to standard method. I feel using grolleg in stoneware is bit of a waste. This can be beneficial to some degree when blending with glazes that contain high % of magnesium or frit. Frit contains oxides predetermined as to quantity and type, which are then melted, fast cooled and ground into a powder. Talc can also affect iron in the clay body, causing a light brown or red tone in high-temperature re­duction clays. Ball Clay FX / CA1 (BA200), Ball Clay R (BA210) or Feeneys Fireclay (BA361). Potters typically constitute less than 0.01% of the producers market.An example of this economic reality is Burns Brick Company, which mined Ocmulgee clay for brick plants. Some raw kaolins, such as Avery kaolin, cannot be readily substituted; however, any kaolin that has been calcined—heated to remove its chemical water (Glomax LL or Ajax- SC)—can be used interchangeably. This item will be permanently deleted and cannot be recovered. A wide array of kaolin (also known as China Clay) products are available. Kiln wash is often made from 50:50 mix of kaolin and silica. According to the data sheets, Grolleg has the more iron of the two. It is al­ways better not to be in the position of needing a replacement material; how­ever, when it is time to reorder materi­als, always be exact as to the chemical name, common name, mesh size, and the name of the mine or processor. Often, ceramics suppliers cannot comment accurately on availability, as they are only a link in the chain of supply. When I do make my clays I use a slurry method. But kaolins have relatively low plasticity when compared to other raw clay types. Be aware that the ceramics supplier orders the material from a processor, and sometimes several processors sell versions of a raw material. Particle size can also affect the de­gree of melting or vitrification that occurs in the clay body. If any additive results in a better clay body with fewer defects, it is well worth the extra cost. Some kaolins make the glaze gel, this is a helpful additional mechanism to keep it suspended. Then I came in to 'do my research' via a question placed on this forum! The most economic way to judge raw materials is through their reliability and ease of use, not their initial cost to purchase. EPK is slightly higher in Titanium, so that can have a small effect, but for the vast majority of glazes it won't matter. Both of these are mixed 70:30 kaolin:feldspar. Many factors can contribute to a reliable clay turning into something different. A smectite blend used as a suspension aid and plasticizer. Rutile is a titanium and iron combi­nation, which produces pale tans, light browns or blue in glazes. Therefore, the effect of a dark- versus a light-firing ball clay will not be significant in the fired result of colored glazes. The darker-firing (due to organic con­tent and other contamination) bento­nites have greater plastic qualities than the cleaner, light-firing bentonites. An example of the same name clay with a different material in the bag is Kentucky-Tennessee Clay Company’s Old Mine 4 ball clay. Once you submit this recipe for moderation you will no longer be able to edit its content. Order-delivery delays are getting longer and longer as the fibreglass industry is making more and more demands on kaolin suppliers. Most kaolins, ball clays and some stoneware clays that the potter uses for clay bodies are air floated. This transformation is also exploited in engobes. Every load of material that they receive has to be checked. Just because the name on the bag is the same doesn’t always mean what’s inside the bag is the same every time. Albany slip», a dark-brown-firing, earthenware type, high-iron clay found in Albany, New York, is no longer being mined. A partial list of ball clays contains Thomas, XX Sagger, Kentucky OM 4, and Tennessee 9. A silty material with very low plasticity, used in glazes as a source of iron. This is because of the variables in­volved when substituting one mate­rial for another, no matter how closely they appear to match. Knowledge of raw materials should be obtained from several sources. Both contain about 40% clay. Moreover, an insidious and some­times subtle change can occur due to geological changes of raw-materials de­posits. A couple of tablespoons of plain yoghurt gets it going nicely in the first batch of slurry. These two samples demonstrate how different the LOI can be between different clays. Always choose a replacement calcium carbonate with approximately the same mesh size as the original. Kaolin is a very refractory aluminum silicate. A source of calcium used as a flux in high temperature glazes. Listed in the chart below are the most com­monly used frits and their equivalents. Of course, this has also eliminated the possibility of getting a truly outstanding single-pit batch of clay. These chunks of metal were pulled out by magnets in the production line, a thousand boxes of porcelain are now garbage. So shrinkage is greater across than along them. Potters make up less than VSY of 1% of the raw material purchasing market in the United States. I'd not heard of the rag trick. Depending on the type of kaolin used, 15-20% should be enough. The larger mesh sand would not melt with the other raw materials, and would also change the handling and throwing characteristics of the clay body. At some point, a large corporation purchased the company and determined that processing, bagging and shipping clay to potters was not profitable enough, so the decision was made to stop production of Ocmulgee clay for sale to potters and ceramics supply companies. Higher percentages can make the moist clay thixotropic (the moist clay body deforms under pressure) and gummy when water is added during handbuilding or throw­ing operations. After that, just mix in some reclaim with any new stuff. There is a huge range in kaolin plasticities, test for yourself to find out. Then we'll make test bars (of all the samples mixed) to fire across a range of temperatures (to compare fired maturity with past shipments). They can con­tain soluble oxides in an insoluble form, while also tying up toxic oxides in safe glassy matrixes. In high-temperature bodies, the lack of a true fireclay component makes the clay less refractory or heat resistant, which can result in warping, shrinking or bloat­ing during firing. Ball Clay FX (BA200)or Ball Clay R (BA210). Whiting, calcium carbonate, is a high- temperature flux that can make a glaze harder; it can also develop a chemically resistant glaze surface. The most severe drawback is the short maturing range; sometimes the clay body can easily be underfired or overfired within a one-cone range. Before mixing any new glaze in your studio, check to make sure all the mate­rials are still available. A fine grained ball clay mainly used in casting bodies. Keep up to date on which materials have changed or are no longer being produced. Ball Clay R (BA210) or Feeneys Fireclay (BA361). Remember, most raw glaze materials look like white or of T-white powder and feel similar to one another. It is interesting that, although the kaolin has a much larger ultimate particle size, it is shrinking much more (23% total vs. 14%). Always look for similarities in both when trying to sub­stitute one material for another. Some have one set of numbers followed by a slash with another set of numbers, indicating the particle size ranges of the grog. In clear or white glazes, dark-firing ball clay can tint or shade the fired glaze. Feldspars fall into three basic groups: potassium feldspars, sodium feldspars and lithium feldspars. While CMC can be used as a glaze suspension aid, its primary function is that of a glaze binder. Each has its own distinctive characteristics, which can influence plasticity, matur­ing temperature, fired clay color and glaze fit. It is used to aid glaze suspension. The ceramics supplier should be able to identify the producer of every raw material. We now have to check every pallet. Clays are often the most variable material that production departments have to deal with. The amount of contamination and the de­fect it can produce in the fired clay body is dependent on the original use of the firebrick. Cal­ cined kaolin can be produced by firing any kaolin past dull red heat—approxi­mately 1100 F. Calcined and regular kaolin can be used interchangeably but the reduced shrinkage of the calcined kaolin can change the raw glaze fit as it dries on the pot.

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