Teacher's Guide to Experiment #1

Clay Labs

Consult the art teacher or ceramics craft shop for firing times.

Materials and Supplies:

•Plaster of Paris may be purchased at some hardware stores. Soft clay (such as is used on a potter's wheel) is available in art supply stores. Do not use the plastic, nonbaking type of clay. Clay slip is available from ceramic craft shops. Both clay and clay slip can be purchased from American Art Clay Co., 4717 W. Sixteenth St., Indianapolis, IN 46209-2292.

•It is recommended that lab tables be covered with plastic or newspaper to simplify clean up.

•A three-point apparatus is designed to support the beams at the ends while applying a force in the middle. This apparatus can be a simple as 2 desks to support the beams and a rope loop in the middle on which to hang weights or a bucket to hold weight.

•A second class lever system could also be set up.

Procedure:

•This procedure is written for each student group to produce one Plaster of Paris mold, one formed clay beam, and one poured clay slip beam. If done this way, two groups will have to work together in Part C with one set of beams having been fired and the other set left green. It is important that all beams be nearly the same size. If variations are desired, adjust time and quantities of materials used.

A-1 •Plaster of Paris may be mixed in mold form or in a separate container and then poured into the mold.

A-2 •The block could be removed shortly after the Plaster of Paris begins to set, or it could be left in the form until the next day.

•A piece of 2" x 2" or 2" x 4" lumber or 1" x 2" firing strips or a plastic form can be used as a block form. These could be marked with a line at 1 cm to get consistency in depth among the student groups. If other objects are used to press into the plaster, they may need a light coating of oil to prevent them from sticking to the plaster.

B-4: •There are a couple of ways that this can be done. One is to press clay into the mold, smooth, and pull out a beam. You may have to run a knife around the edge to help remove the beam. Or the block form could be used as a template to cut a beam from a slab cut off the stock clay (try to cut off slabs to just the right thickness) or rolled to the right thickness. Test tubes or graduated cylinders make nice rolling pins.

B-6: •This might be about 30 minutes or more. The poured beam could also be left in the mold until the next day .

B-7: •Students are instructed to find the density through mass and linear measurements of the beams when they are first made, after air drying, and after firing. Additional measurements could be added to get a more detailed picture of the changes that occur during these processes.

B-9: •If a large ceramic kiln is used, it may take 20 minutes to load the class items into the kiln and several hours to bring the kiln up to temperature and then overnight for it to cool back down. If a small enameling kiln is used, the process may take only an hour or so.

•It helps if the beams are prewarmed and dried at about 200oF in a regular oven for 2 to 4 hours before firing.

•The beams to be fired are to be dried, either for several days in a warm dry place or several hours in a drying oven at 100oC.

•Put the object in a kiln and the raise the temperature slowly until the maximum temperature called for is reached and held for several hours.

•Turn the kiln off and allow it to cool before opening. If a ceramic kiln is not available, it is possible to use an electric hot plate with an 8 inch clay flowerpot lined with aluminum foil and inverted on the plate. This small kiln will give a temperature around 1300oF. This really works!

C-12: •If the 2nd class lever system is being used, then measure the basic down force by hooking a spring balance to the end of the lever arm. If a bucket on a rope is being used, make sure they are the same for each test group or record the different masses.

C-14: • If a second class lever was used, add the basic force of the lever arm and this is your effort force. Multiple this force by the IMA (Ideal Mechanical Advantage) of the machine. You will have the force that was needed to break the beam.

•You may want to do a 3-point test or thermal lab on other materials like glass (Pyrex), plastic, and metals for a materials comparison.

Answers to Questions:

1. Firing fuses the particles together.

2. The water that was still in the pores might cause the beam to break.

3. Strength is the ability to resist deformation, hardness is the ability to resist

abrasion.

4. Answers will vary. Basically unfired beams are more dense, less thermally

conductive, and weaker than fired beams.

5. Too Low - objects would crumble. Too high - objects would be melted down

like glass.