elizabeth priddy on mon 27 dec 99
the numbering system for cones is about the
most asinine thing I have ever encountered in
clay.
If you describe it as a number line with 00 at
the middle, you can make people understand it
easily enough, but for the rest of the world,
the '0' when placed before a number is
meaningless and dismissed. This is why they
do this.
This is vague, but I don't want to diseminate
misinformation so I won't declare that the
something I am referring to is lead, maybe
someone can clarify this detail for me:
I think that cone 0 is supposed to be the
particular melting temperature for something
and that everything else was named relative
to this particular point, but it sure seems
like someone would have changed this at some
later, but pre-modern, time.
I, unfortunately, think it is too late and
we are stuck with it.
---
Elizabeth Priddy
email: epriddy@usa.net
http://www.angelfire.com/nc/clayworkshop
Clay: 12,000 yrs and still fresh!
On Thu, 23 Dec 1999 14:03:09 Nancy Guido wrote:
>----------------------------Original message----------------------------
>I have been fortunate to work in two elementary schools and one high school
>as a visiting artist. The most peculiar thing I have encountered is the
>teachers" misunderstanding of the cone temperatures. In all three instances
>I was told the glazes were cone 5. When I saw the clay was rated only to
>cone 1, I questioned this. They looked puzzled until I explained the
>difference and showed them the chart. Even though the differences between
>cones is not great, the difference between cone 5 and cone 05 is a biggie.
>
>Nancy G.
>
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Tom Buck on wed 29 dec 99
Ms. Priddy:
The "0" in Cone Numbering arose empirically. If I read it
correctly, the numbering system has to do with Hermann Seger's invention
of Pyrometric Cones, and his way of describing a glaze mix: 1 mole of flux
oxides combined with alumina (0.1-0.6) and silica (1 - 10+ moles).
Parmelee describes how this works in his chapter on Conversion of the
Batch to the Glaze.
Given CaO as 1, and Al2O3 as one-tenth of SiO2, then the Cone
Number designation reflects the moles of SiO2 in the Pyrometric Cone's
composition. But since this is NOT a straight-line relationship
throughout, there occurs a discontinuity, which is why the "0" was
introduced.
Perhaps others can make better sense of this.
Tom Buck ) tel: 905-389-2339
(westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street,
Hamilton ON L8T 3E1 Canada
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