Often when a raw material is no longer available, it remains in abundant supply but is simply not economically viable to mine and distribute. Feldspar, one of the most common materials found in glazes, can be classified into three groups: potash feld­spars (Custer, G-200, K200 and Primas P—no longer available are Buckingham, Oxford, Yankee, Clinchfield #202, Key­stone, Maine, Madoc H, A-3 and El- brook); sodium feldspars (Kona F-4, Nepheline Syenite 270x, Nepheline Sy­enite 400x, Calspar, Primas S, NC-4, Unispar 50, C-6 and Minnspar 200— no longer available are Eureka, Bainbridge, #56 Glaze Spar, Lu-Spar #4, Minpro #4 and Clinchfield #303); and lithium feldspars (spodumene, lithospar and petalite—lepidolite is no longer available). The top one is vitrified, the bottom one will not vitrify for another 15 cones. Raw material “drift” can also bring about the need for substitution. These materials have low alkali contents (especially the kaolin), this lack of flux means they are theoretically highly refractory mixes of SiO2 and Al2O3. HERE is an interesting thread from Clayart in which Ron Roy discusses kaolins with some other tech guys. big thanks to ^ that guy. Some red copper oxide always floats on the liquid glaze surface but does not affect the color or texture of the fired glaze. A silty material with very low plasticity, used in glazes as a source of iron.   You cannot paste images directly. Ibex-200 is a dark-firing bentonite that can be used in darker colored glazes. The smaller the particle size, the less opacifier is required in the glaze recipe. The number of different materials is de­pendent to some extent on the func­tions the clay body must serve. Moreover, an insidious and some­times subtle change can occur due to geological changes of raw-materials de­posits. Not listed are materials that do not have a practical substitution or would involve exten­sive clay body testing for the purposes of substitution. With ball clay and other stuff in there you won't really notice much of a difference in feel or color anyway. It is, by far, the most plastic kaolin available in North America. Several other factors can hinder the substitute material from yielding similar results, such as a difference in the materials particle size, chemical com­position or processing methods. Eg om4. Decorating Slips, Engobes, and Terra Sigillatas. A secondary water-washed kaolin mined in Florida. Feldspars fall into three basic groups: potassium feldspars, sodium feldspars and lithium feldspars. The bottom one is New Zealand kaolin, it loses 14% when fired to the same temperature! I'm thinking that you are wrapping clay in a moldy rag to get some organics in there. In clear or white glazes, dark-firing ball clay can tint or shade the fired glaze. Sometimes, a material will act differently in the studio than is re­ported on the written page. Ball Clay FX (BA200)or Ball Clay R (BA210). While a precise equivalent material will not be possible in all situations, the substitu­tions listed here will work in a high percentage of glazes. Used in amounts of 0.25% to 2%, based on the dry weight of the clay body, barium carbonate prevents scumming in the fired ware. This transformation is also exploited in engobes. Westerville, OH 43082, © 2020 The American Ceramic Society, all rights reserved. In the mid 1970s, OM 4 was mined from a single pit of clay. Most often, trying to save a mistake will result in more unusable clay taking up room in the studio. Raw materials and clays that were not included either do not have a practical substitution or involve glaze calculation to arrive at a close material match. Occasionally, the changes occur almost imperceptibly, but after a while the total of small changes can push the clay into a problem-producing state. That means the kaolin is generating them and the Gerstley Borate the larger bubbles. Ball clay contributes silica and alu­mina to the glaze formula. Wondering how substituting Grolleg in both clay & glaze recipes with EPK will effect results. For example, [Thomas ball clay and Taylor ball clay] are both light in fired color and can be readily substituted for one another in a clay body. i picked these two for the similarity in materials and therefore cost. As the clay body matures, the dark ball clays iron and manganese component becomes more visible. Where translucency and whiteness are paramount, highly plastic kaolins and white burning ball clays and bentonites can be used . A partial list of ball clays contains Thomas, XX Sagger, Kentucky OM 4, and Tennessee 9. Quantity discounts are available.. . Strangely, non-plastic kaolins are not necessarily whiter burning. 65% Ball Clay R (BA210) blended with 35% natural red iron oxide (BA501) Bell Dark Ball Clay. For example, Edgar Plastic Kaolin (EPK), a secondary clay (transported by wind or water from its original site of formation) that has been mined in Putnam County, Florida, since 1892, is used in the manufacture of spark plugs. [Red iron oxide (approxi­mately 90% Fe203) and Spanish red iron oxide (approximately 81% Fe203)] are almost identical in their effects on clay body color. This will en­sure the optimum glaze match. The higher amount of iron and manganese in each type of ball clay will contribute to a darker fired ball clay color. Keep in mind the synthetic brands of iron oxide can be stronger than natural iron oxide ores and a one-to-one substi­tution will not always produce an exact match. Most kaolins, ball clays and some stoneware clays that the potter uses for clay bodies are air floated. Grolleg, however, vitrifies at a lower temperature so you can get more of it into a translucent body than with EPK, which improves workability. The ceramics supplier should be able to identify the producer of every raw material. Today I was mixing some glaze tests and there was mention of both grolleg and EPK within some of my test recipes. It is produced in various mesh sizes under different trade names by many companies. Many porcelain clay bodies contain as much as 50% kaolin, so choosing the cor­rect kaolin substitution is critical in producing a successful result. Questions about your account? When developing a clay body, be sure to contact the mines and raw material processors to determine how stable supplies will be in the future.