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Lesson Plans

Re: 60 kids down my throat!

[ Thread ][ Subject ][ Author ][ Date ]
Dianna (dmammone)
Thu, 12 Nov 1998 20:47:28 -0500

With results like that, almost all your pots breaking, I would look to a
firing problem rather than air bubbles. If it is air bubbles there should
be shards EVERYWHERE and lots of them should be small size. Sounds like you
are running in to trouble around 600* degrees when what we call "quartz
vitrification" occurs. That is the point when the MOLECULAR WATER is
driven out of the clay and that radical chemical reaction occurs. At that
point the clay can not be turned back into mud again. Try leaving you kiln
lid up longer, like 2-3 hours, then propping it open with a 2 inch wedge for
30 minutes. Then extend you firing times and don't put any of the peep hole
plugs in until you can see it is red hot. Then fill them in slowly working
from the bottom to the top. This is a VERY safe, (over protective) way to
do a firing. Sculpture is much harder to fire than wheel work. Handbuilt
pieces are full of thick and thins, etc.

You can also look into switching clay bodies. Find one that is a sturdy
stoneware with a little grog mixed in. It should tell you in the
description of the clay. Grog is clay bits that have been fired and are
ground very fine and remixed into the clay. It helps the clay body stretch
as it expands and contracts in the kiln. You can buy grog cheaply and wedge
it in to your present clay. Comes in several grits, fine usually works well
with kids. Ahhh...pottery, such a mystery. Let me know if I can help you
further. Great book to get is "Clay and Glazes for the Potter " by Daniel
Rhodes. It's the "Bible" of clay. It's a challenge to understand all the
info that is in it, but if you go at you're own pace, you'll catch on.
Good Luck----Original Message-----
>After firing 60 pinch pots yesterday, I opened the kiln to find small
>pieces of shattered clay. Only 2-3 pieces survived without a crack.
From: Michelle H. Harrell <mmhar>
To: <>
Date: Thursday, November 12, 1998 12:49 PM
Subject: 60 kids down my throat!

>Help! I've just ruined 60 twelve year olds day!
>After firing 60 pinch pots yesterday, I opened the kiln to find small
>pieces of shattered clay. Only 2-3 pieces survived without a crack. I
>had been careful to explain to them to wedge the clay for air bubbles.
>We let it get bone dry and I loaded it into the kiln. This is the 2nd
>time I've fired greenware but I following the same directions I did the
>first time which were left by the previous art teacher. I left the lid
>cracked open the first hour set on 1 (cone 5). Then I raised the temp.
>3, 6, 8, hi, every hour.
>This is an old kiln and no manual was left for it. I know I could call
>the company and get another manual. I'll work on that.
>Can any of you help me? I probably sound like an idiot to any of you
>who know what you are doing. I know its probably the temp. that I'm
>firing it at.
>Back to breaking hearts of babes,
>Michelle H. Harrell
>North Garner Middle School
>Garner, North Carolina
> * ~ "The artist must train not only his eye but also his soul."
> ^
> \_/ -Wassily Kandinsky
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