Clay Making Lesson Plans - Testing Clay Bodies

Clay Making Lesson Plans - Testing Clay Bodies

Fundamental clay making lesson plans should consist of teaching students the properties of various clay bodies. Some clay bodies shrink less; other people have far more or less absorption; some bodies have higher or lower maturation points; and of course, clay bodies come in a wide selection of colors. Although the hundreds of kinds of commercial clays available from suppliers are described rather well in the catalogs in terms of what they are and what they can be utilized for, nonetheless really working with them and firing them raises particular problems which can only be resolved by actual testing. Students need to learn early on how to test clay bodies in order to realize their material - its possibilities and limitations.

Testing a clay body gives a terrific deal of data which can be observed, felt and touched 1st hand in the studio. Whilst catalog photos and art lesson plans show how bodies might appear when fired at various cones, they could not reveal precisely what the clay will do at the particular cone to which you are firing. A basic clay bar test gives specific data relevant to the projects at hand. A 25 lb. sample is generally sufficient to complete all the tests required. In order to yield a wide range of information about the clay body, tests must be run at diverse temperatures, since even if only firing to a particular cone is contemplated, still the outcomes from firing at other cones can prove helpful in the future. The three most critical characteristics of clay bodies are shrinkage, absorption, and slumping / warping. It is also important to note color, plasticity, texture, and hardness.

When firing at higher temperatures than recommended (whether by mistake or purposely), clay bodies melt and fuse to the shelves. In testing clay bars a shallow firing box is needed to protect the shelves of the kiln, as well as to make for simpler handling. Clay stilts are also required for a warping test. Make uncomplicated clay boxes out of high-fire clay, 8" to 10" square with 1" walls. Make triangular stilts about as thick as a little finger, and sufficiently long to span the clay bar's width.

For each clay body being tested, 3 clay bars are required, roughly " thick by 2" wide by 6" long. If the students' work projects will be thicker, then the bars ought to be made to that thickness (but not exceed " in any case). After cutting the bars, draw a 5" lengthy line on 1 of the bars with a hash mark at each of the ends, to be utilized in the shrinkage test. The bars ought to be left until they are bone dry. Measure the shrinkage lines on the bars to see whether or not they have changed from the original 5" length. Place the bars side-by-side in the firing box, and put 1 of them (with out shrinkage line) on triangular stilts. The 1 on stilts is employed to figure out warping or slumping. Begin firing at lowest cone temperature, and then refire the bars at higher cones, until the projected highest cone is reached. For example, sample bars to test for a cone 10 body may well be progressively fired at cone 06; cone 01; cone 6; and at last cone 10.

Testing is simple, and is fundamental to ceramic art education. Color change and surface texture change can be determined visually. Hardness can be determined by scratching with a nail. This test is utilized to decide the durability of the surface at diverse firing temperatures. The bars can be examined visually for warping or slumping in the center: remove the bars from the stilts and place on a table top upside-down so that the height of the slump can be measured. This test indicates at what temperatures the walls may well start to warp, or a plate may start to slump. Shrinkage can be determined by measuring the length of the lines on the shrinkage bars. Understanding the rate of shrinkage is helpful in determining which bodies can be used together, and which glazes will work for the body. To decide absorption, two tests can be utilized: simple visual inspection, and weight calculation. Put a few drops of ink on the bar surface to stain it. Enable it to soak in for a few hours, then wash the surface with water. The darker the remaining stain, the far more absorbent the clay. For additional specific measurement, weigh the fired bar; then soak the bar overnight, pat it dry, and weigh it once more. The distinction between the two measurements is the weight of the absorbed water, which is divided by the original dry weight of the bar to obtain the absorption rate.Kingston used cars

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