Lorraine Pierce on sun 12 mar 00
Hi Tom, this post is in regard to your article in Digitalfire, 1/25/00,
Synthetic Gerstley Borate. You had formulated two 1000 gram test batches of a
mix to emulate Gerstley Borate,but had not tested it as of Jan.24...Do you
have anything to report on your tests as yet?
I am just starting to get aquainted with the Insight program, but have a long
way to go. In the meantime, I have mixed 28 ^6 oxidation glazes that contain
no gerstley borate, (from the Clayart archives), and when my glaze tests come
out of the kiln Tuesday I may find myself tempted to forget gerstley
borate...!! Thanks for all you share with us 'claybuds'. Lori in New Port
Richey, Fl.
Tom Buck wrote:
> ----------------------------Original message----------------------------
> mel....many claybodies contain too much of minerals/chemicals that lead to
> bloating/dunting if overfired. i recall one body i threw years ago that
> weeped at C3, was tight at C5/6 and bloated at C7+ Why? Because it
> contained a significant amount (10%???) of nepheline syenite, a mineral
> with high sodium oxide and, compared to other feldspathic minerals, less
> silica. Common feldspars (G200, Custer, F-4) have a crystalline structure
> that can be expressed in simple chemical terms: 1 mole flux oxides to 1
> mole alumina to 6 moles silica. Neph sy is 1:1:4 approx.
> Another factor is the possibility of formation of cristobalite, a
> crystalline (structured) form of silica. Perhaps Ron Roy will say once
> again how overfiring or very slow cooling will lead to cristabolite and it
> in turn making the claybody more discontinuous and easily broken.
> There are also bodies with unusual high amounts of iron compounds,
> or titanium compounds, and perhaps fluorine compounds. Under certain
> firing regimens these compounds could lead to failed pots, and refiring
> would certainly enhance this effect.
> There, that's all I want to say for now. Let Michael, Ron,
> Evan, Mary et al come forth and add to the discussion.
> til later. Peace. Tom B.
>
> Tom Buck ) tel: 905-389-2339
> (westend Lake Ontario, province of Ontario, Canada).
> mailing address: 373 East 43rd Street,
> Hamilton ON L8T 3E1 Canada
>
> On Fri, 10 Mar 2000, mel jacobson wrote:
>
> > ----------------------------Original message----------------------------
> > according to older data from japan, a single re/fire does
> > not do any damage to the clay body. mr. uchida re/fired
> > about 30% of his pots. (of course one pin hole in a pure
> > white pot looked like hell.)
> >
> > he often told me that a second or third re/fire would break down the
> > integrity of the clay body.
> >
> > perhaps one of our chemist/engineers could clarify this point.
> >
> > mel/mn
> > http://www.pclink.com/melpots (website)
> > from minnetonka, minnesota, u.s.a.
> >
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