[Clayart] Wide range clay

David Woof woofpots at hotmail.com
Sat Jan 22 20:30:37 UTC 2022


So right re Bone China Robert.   There are notes in older text books re firing translucent porcelain stating that to truly reach that glass-like translucent state of vitrification the vessel was fired while packed in pure silica sand to support the form from slumping.

I have oxidation fired "Tite Red Bodies" at cone 6 that ring like a bell and come in tested at 0.4 absorption.

However, at cone 6 down, the foot rings were beginning to "Pluck" meaning they were becoming Glassy enough to pick up ("pluck") tiny bits of shelf wash clinging to the foot rings.

Excellent body, I just needed to adjust the firing schedule to back off to a 0.7 % absorption.

Misneach,
Woof>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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From: Clayart <clayart-bounces at lists.clayartworld.com> on behalf of Robert Harris <robertgharris at gmail.com>
Sent: Saturday, January 22, 2022 10:07 AM
To: Clayart international pottery discussion forum <clayart at lists.clayartworld.com>
Subject: Re: [Clayart] Wide range clay

David, while I agree with you almost wholeheartedly, I will add the
exception that proves the rule. Properly formulated and fired bone china
really is fully vitrified. Now obviously that almost certainly means
commercially produced, but from my reading it's very close to glass.
Now arguably bone china stretches the definition of "clay", but ...

On Sat, 22 Jan 2022 at 09:56, David Woof <woofpots at hotmail.com> wrote:

> "I don't recall if he gave any reasoning. " James said.
>
> Weigh on gram scale and subsequently Boil a bisqued slab bar in water for
> four hours.  Then high fire to intended cone. (not to a set temp) use a
> cone as true "Heatwork" Baseline. Weigh again and do the math for
> percentage of absorption.
>
> My clay​ body absorption % must be 1.5 or less depending on the
> constituents of the body.   I prefer 1.0 to a 0.5.
> ​Some bodies will leak if there is one half cone variance if kiln is
> firing unevenly between zones and the firing didn't take the clay into the
> middle of the proper vitrification zone.
>
> And "Completely Vitrified" is a non-accurate description of properly fired
> clay..  As in Like "Kind of Pregnant" or "Kinda happy" etc etc.
>
> When I hear "Completely Vitrified" it sets my teeth on edge because that
> condition in clay would be a melted slumped gob or pool that no longer
> resembles a functioning vessel.
> (Snake oil and paregoric for what ails ya)
>
> Misneach,
>
> Completely Woof......................................or at least 1.5
> %........some days...............................
>
> ************************************************************************************************************************
> ________________________________
> From: Clayart <clayart-bounces at lists.clayartworld.com> on behalf of James
> Miner <woodfirejim at gmail.com>
> Sent: Friday, January 21, 2022 12:54 PM
> To: Clayart international pottery discussion forum <
> clayart at lists.clayartworld.com>
> Subject: Re: [Clayart] Wide range clay
>
> Regarding acceptable porosity of fired clay for functional ware, I talked
> to one of the head people at a large clay company many years ago to find a
> good body for cone 10, and he said it should be 2% or less.  I don't recall
> if he gave any reasoning.  I won't give you the names involved in case I
> have misremembered, but I still go by that myself.  YMMV.
>
> Anybody else have a different answer?
> Jim
>
> On Fri, Jan 21, 2022 at 10:34 AM Vanessa Greene <bequiet at att.net> wrote:
>
> > Any thoughts from all you experienced potters about those clays that are
> > marketed as a wide ranging temp clay, cone 6-10…..are they really fully
> > vitrified at cone 6? I hear very different opinions about this…..what
> > absorption rate is necessary for functionally food safe pots?  (
> > continental clays B clay, Buff etc…. )
> > I have always fired these clays to cone 10 but some people suggest that
> > these clays are suitable for both cone 6 and 10 firings. Thoughts?
> >
> > Vanessa Greene
> >
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