[Clayart] Wollastonite/hardening clay bodies

Paul Gerhold gerholdclay at gmail.com
Thu Jul 20 16:11:18 EDT 2017


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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