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Posted by DKat on October 16, 2007, 9:58 pm
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>
> "Bubbles_"
>
> <<I have seen a lot of potters throwing pretty uncentered pieces,
> but I wonder if the middle is uncentered or just the outside?>>
>
> Remember that the clay on the spinning wheel will want to travel outward,
> so
> you need to keep squeezing inward as you raise the walls. Wobbles can
> be worked around, but it's always better to spend some additional time to
> minimize them -- they're becomes especially painful when you're trimming
> :-)
>
> <<PS - asked my dealer about cones, and he doesn't carry them and doesn't
> find
> them useful at all. Will try to remember to talk with my teacher about it
> on
> Friday.>>
>
> I don't like being blunt but your dealer's an idiot. There's no way to
> measure
> heat-work except through the use of cones. I use a pyrometer and cones,
> but
> the pyrometer's just to give me an estimate of heat, it cannot tell me the
> amount
> of heat-work being done on the clay -- that's what cones are for. They're
> invaluable in repeating firings, especially when the kiln load is
> significantly
> different between firings; the cones will allow you to consistently repeat
> your
> firings (plus alot of other things). I can easily fire wihout the
> pyrometer, but
> certainly not without cones.
>
> Best -
> Peter
> NM
>
I agree with Peter 100% on this. Sure you can fire without cones but it is
not wise. For example you stated that you soaked for 40 minutes. There is
no way you can know what the heat work was that you reached without cones.
As I said, I dropped my temperture by 10 degrees F to get the heat work I
needed with a 30 minute soak. You said that you suspected that you were
firing 20 degrees C less than what your kiln said it was doing. That is a
huge amount. This is something you should know and cones will tell you.
About centering - I can't imagine someone throwing an acceptable pot if it
is not centered. First off, take as much work out of the process as you can
by patting to center.
I love this UTube - his clay before he even begins throwing is a work of
art.
http://www.youtube.com/watch?v=PxyZ6qk0w34&feature=PlayList&p=2FCA2FA4A36684E1&index=1
Always remember to remove your hands slowly from the clay when you have it
centered or else you risk knocking if off center as you move away.
When you think that the piece is centered check it with a needling tool -
both sides and top. If it is centered, do your initial opening. Now check
to see if the opening is centered with your needling tool (you are using
your needling tool the same way you do when you are checking if your are
centered for trimming. If both the outer an inner walls are centered and
you are getting wobbles you have two things left. When you opened up the
floor you did not maintain the level of your fingers as you pulled out and
you opened slowly enough that your floor is not level (really hard to do but
possible). The other is that you have air bubbles in the clay. Large
enough ones will make your walls uneven.
http://www.youtube.com/results?search_query=centering+clay
But what it all comes down to is doing it over and over and over. 5000
hours you will be a professional (that is the time estimate from
Psychologist Don Norman)!
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