[Clayart] Wollastonite/hardening clay bodies

M Gordon clayart at earthlink.net
Thu Jul 20 21:25:46 EDT 2017


I remember a show about very large clay panels being made (I think in  
China ) so large it was hard to believe they could be handled. Mike  
Gordon On Jul 20, 2017, at 1:11 PM, Paul Gerhold wrote:

> I remember an article about that as well.  If I remember correctly  
> they were poured panels.  Wollastonite is also used in commercial  
> tiles to allow fast firing and cooling.
>
> I only posted originally on Wollastonite long ago because there were  
> people posting about hard throwing clay in bags.  Removing the 5% of  
> Wollastonite from my body solved that problem with no noticeable  
> difference in the final body.  I was not trying to say there is no use  
> for Wollastonite in ceramics, just that in small amounts in a throwing  
> body the disadvantages can vastly outweigh any possible benefits.
>
> Paul
>
> Sent from my iPad
>
>> On Jul 19, 2017, at 9:14 PM, Bryan Johnson <bryj at cheqnet.net> wrote:
>>
>> I remember seeing work being done on a 50 : 50 ball clay wollastonite
>> body.  They were making very large panels that were somewhat flexible.
>>
>> Bryan Johnson
>>
>>> On Wed, Jul 19, 2017 at 6:40 PM, Paul Gerhold  
>>> <gerholdclay at gmail.com> wrote:
>>>
>>> Well the opinion I stated on Wollastonite comes from Jon Pacini at  
>>> Laguna
>>> who probably has an inarguable knowledge of clay ingredients.  My
>>> experience just confirms what he said about Wollastonite causing  
>>> clay to
>>> harden in the bag while not actually contributing any particular  
>>> benefit to
>>> the body.  Opinions may differ but his has proven out in my  
>>> experience.
>>>
>>> Paul
>>>
>>> Sent from my iPad
>>>
>>>> On Jul 18, 2017, at 5:22 PM, David Woof <woofpots at hotmail.com>  
>>>> wrote:
>>>>
>>>> Paul,
>>>>
>>>> our experience is obviously different, of course there are many
>>> variables related to the other mineral constituents when combined in  
>>> a
>>> particular clay body formula and the water one used as well.
>>>>
>>>> So before laying too much pro or con at the feet of  
>>>> wollastonite........
>>> we must tread softly....yet push ahead in our quest for Ceramic  
>>> knowledge.
>>>>
>>>>
>>>> I had hoped to stimulate thought and possible conversation re the  
>>>> last
>>> paragraph of my post:
>>>>> Wollastonite offers much more to a clay body or glaze than simply  
>>>>> as a
>>> convenient source of, or substitution for, calcium and silica.  
>>> ***It's
>>> aricular structural character provides a dimensional stability and  
>>> flexural
>>> modulus to the materials it is added to.****  It is not >difficult to
>>> translate this to beneficial reasons for application in our glazes  
>>> and clay
>>> bodies, before, during, and post firing.
>>>>
>>>>
>>>> However; since many folks now buy ready made box clays, subsequently
>>> don't much care what is in the clay as long as it works the way they  
>>> like
>>> it or willing to suffer through with it, and us few who know our  
>>> materials
>>> and formulate accordingly, there is probably scant interest in  
>>> conversation
>>> about what we think we already know!!!!    So Tally-Ho Mates!!! the  
>>> fox is
>>> hiding in the hen house, licking his flexural modulus, and yawning  
>>> his fox
>>> in the hen house grin.
>>>>
>>>> Misneach,
>>>>
>>>> David
>>>>
>>>> ***************************************************************
>>>>
>>>> ________________________________
>>>> From: Clayart <clayart-bounces at lists.clayartworld.com> on behalf of
>>> Paul Gerhold <gerholdclay at gmail.com>
>>>> Sent: Friday, July 7, 2017 2:46 PM
>>>> To: Clayart international pottery discussion forum
>>>> Subject: Re: [Clayart] Wollastonite/hardening clay bodies
>>>>
>>>> That may well be but when I eliminated the 5% wollastonite from my  
>>>> clay
>>> body, as recommended from a post asking for  help on Clayart, the  
>>> body
>>> stopped becoming hard after a few months in storage with no  
>>> discernible
>>> change in throwing properties and no change in raw or fired strength.
>>>>
>>>> And the body was mixed very soft in an attempt to overcome the
>>> hardening. That did not work.
>>>>
>>>> Paul
>>>>
>>>>
>>>> Sent from my iPad
>>>>
>>>>> On Jul 6, 2017, at 3:40 PM, David Woof <woofpots at hotmail.com>  
>>>>> wrote:
>>>>>
>>>>> Wollastonite is a valuable material, though still often under  
>>>>> rated and
>>> misunderstood.  What is needed is a working understanding of the  
>>> mineral
>>> composition and characteristics of raw materials useful in  
>>> ceramics.,m
>>>>>
>>>>>
>>>>> Wollastonite is a hygroscopic material and so absorbs water, other
>>> materials including clays such as Hawthorne Clay and grog also absorb
>>> significant quantities of water during post mixing of the clay body.  
>>> The
>>> simple trick is to pug it wetter than useful and "age" while the  
>>> absorption
>>> reaches stasis.
>>>>>
>>>>>
>>>>> Wollastonite offers much more to a clay body or glaze than simply  
>>>>> as a
>>> convenient source of, or substitution for, calcium and silica. It's
>>> aricular structural character provides a dimensional stability and  
>>> flexural
>>> modulus to the materials it is added to.  It is not difficult to  
>>> translate
>>> this to beneficial reasons for application in our glazes and clay  
>>> bodies,
>>> before, during, and post firing.
>>>>>
>>>>>
>>>>> Woof
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> ________________________________
>>>>> From: Clayart <clayart-bounces at lists.clayartworld.com> on behalf of
>>> Paul Gerhold <gerholdclay at gmail.com>
>>>>> Sent: Wednesday, May 10, 2017 7:12 AM
>>>>> To: Clayart international pottery discussion forum
>>>>> Subject: [Clayart] Hardening Clay
>>>>>
>>>>> Back about ten years ago I had developed a really ( in my opinion)  
>>>>> good
>>> Raku body with one major issue.  While it was perfect for throwing  
>>> when
>>> first mixed after a month or so it became so hard in the bag that
>>> additional water had to be added to make it throwable.  I posted the
>>> formula on Clayart and while I got many suggestions the correct  
>>> answer came
>>> from Jon  at Laguna who said my problem was the 5% Wollastonite.   
>>> Once the
>>> Wollastonite was removed the clay stayed throwable in bags for a  
>>> long long
>>> time and there was no negative repercussions caused by the removal.
>>>>>
>>>>> Don't know if any of the problem clays mentioned so far have
>>> Wollastonite but thought this might help someone.
>>>>>
>>>>> Paul
>>>>>
>>>>> Sent from my iPad
>>>>>
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