Sierra Middle School
Riverside, California
(951) 788-7501
Mr. J. Myers
Art Teacher
[email protected]
http://www.rusd.k12.ca.us/ourschools/sms/
Clay and Kiln use
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Clay and Kiln use
The clay used should be a “low fire” variety. Firing at about come 07 to 05; cone 06 is what is desired. This only costs about $9 for 25 pounds, in 2003. This is enough for about 20 people. The finished objects are about the size of a large, child's, fist.
The clay can be in solid, bagged form for hand building, or in slip, a liquid form, for the mold process. This is a bit more expensive per object made at about 70 cents each versus 45 cents. However, this cost depends on the size of the cast object.
Slip Use, (molds)
The objects made should be no thicker than about 1/4 inch. Yes, you can push it, but there is the risk of shattering or exploding, in the firing process and a risk of warpage when it dries.
The Slip process is done by rubber banding the mold parts together and pouring in the slip. It is then timed before pouring out the remaining slip. During this time the plaster mold is absorbing moisture from the slip, thus hardening it somewhat. After the “right” amount of time goes by, pour the slip into a cup. Now let the mold harden some more. When it looks “right” then carefully remove the bands and the parts should be gently pulled apart. Set the clay form on a plaster bat to further harden. At some point you will have to trim away the mold lines and any imperfections. Don’t forget to remove the excess “high hat” that forms where the slip was poured in.
Always have the artist put their Full name and date, including the year, on the object somewhere. All objects look alike at a later time. Use a needle to scribe it.
Detailing
Almost any object can aid in the building of your artwork, whether it be handbuilt or slip cast. God gave you ten good tools, and your mind can supplement those with pencils, sticks, forks, paper clips, needles in sticks, keys, and so on. The main idea is to use these items to push and pull the clay for you. They can also be used to apply designs and textures where “your ol' fat fingers” just won’t fit.
Hand building
Any shape desired can be made if you keep in mind the moisture content of the clay that you are working with and the weather conditions. The more humid, the better, for the clay stays consistent. The drier it is the harder it is to keep all parts of the clay used the same, the “same” being the amount of moisture. You want the clay the same because there is shrinkage when clay dries. If the moisture contents are too different the one with the more water will shrink more. “So what!?”, you say? When things shrink at an uneven rate they fall apart. So much for that 8th wonder of the world you just created!
The objects made should be no thicker than about ½ inch. Yes, you can push it, but there is the risk of shattering, exploding, in the firing process.
Always have the artist put their Full name and date, including the year, on the object somewhere. All objects look alike at a later time. Use a needle to scribe it.
Firing
All clay objects should be dried about 24 hours at a minimum. Yes, you can push it with different weather conditions. Yes, you can use fans; the sunshine, the summer swelter and you can even put the clay in the kiln and turn it on the lowest settings for overnight. You want the clay to be as dry as possible because the firing process turns the water to steam. Ever see a potato in the oven without holes poked in it? Instant mashed spuds, No? Yes, the same thing will occur if you fire the kiln too fast. Experience is the best guide.
Experience is the best guide to knowing what the “right” amount of time for the slip to set, the “right” time to remove the molded object: the “right” thickness to fire. After a while you will KNOW what is “right” and you’ll do it. There is no other way to learn it, I’m sorry. Just charge right on in and do your best, that’s the most fun and informative way that I know of.
When the clay is “just right”, or you’ve run out of time, you load the kil. Both spellings are correct, by the way. If you remember this adage “a kiln packed tight fires right” then all will go well. You can stack all sorts of greenware (unfired clay items) and no harm will befall them, unless you stack so much that is squishes the bottom ones and breaking occurs. One firing is all you can do in 48 hours anyway. Just load away and add shelving as you go. Once again, experience is the best teacher. Push your knowledge by building bigger, thicker, and thinner. Push loading by cramming more in, less in, and so on.
Once loaded close the lid and set the timer. Put the temp on the lowest setting possible and leave overnight. In the morning, around 8, turn up the setting to the next notch. In 3 hours, or so, turn to 50% power. In another 2 hours turn to 100%. Experience will tell if you have pushed it too fast. The first time segment is when the most moisture is present, and the most likely time that things will go “pop”. Oooooops. If that happens, back it down and be more patient! You should NOT hear small sounds. You’ll KNOW what is correct. Once you are at 100% it will take about 2 to 3 hours to finish. The kiln timer should turn the kiln off for you. But, if you are around, you can. I always let it do the job for me, AND I always check it to be safe. Do you like fires? Neither do I. That is why I said overnight. This entire process, if started in the afternoon around 3, on day #1, is completed about 1pm day#2. The kiln is SO hot that it will take about 12 hours MINIMUM to cool. That makes it about the morning of day #3 to remove the items. Again, experience allows me to be able to push the process by starting the firing in the morning, and turning the kiln up that night. And I mean night. Like 2 to 3 am. The process kicks off around 4 am and then by noon I push it and put the kiln’s lid ajar a bit to let it cool rapidly. By about 3 pm I can remove the 300 degree items. It can be done, but is not the preferred route. Items can break when rapidly cooled. Fingers are burned when you think, “I’ll bet I can unload this now”, oops, nope. Ouch, drop. Sorry.
Remember that you are using 240 volts of power. It will curl your hair if not careful. Remember that you are using, at peak temperatures, 1800 degrees Fahrenheit. That’s enough to burn down the forest. If you treat it with respect, there is no problem. Remember that cars are as powerful and hundreds of horses. We don’t worry about them, now do we? (No, but we should!!)
The entire clay experience is wonderful. It gets you, literally, in touch with your creation, and with your creator. God’s world is his, and her handiwork is visible for those who know how to see it. Remember that the Bible makes reference to “the mark of the potter’s thumb”. How will others view your work?
