[Clayart] Wollastonite/hardening clay bodies

ronroy at ca.inter.net ronroy at ca.inter.net
Fri Jul 7 13:47:25 EDT 2017

Just a word of warning on using other fluxes for high fired clay  
bodies - stick to sodium and potassium and perhaps lithium.

The use of the alkaline earths (calcium, magnesium, & barium) in high  
fired clays (above cone 6) can result in cristobalite production which  
can result in dunting - especially in ovenware.


Quoting David Woof <woofpots at hotmail.com>:

> 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.
> 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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Ron Roy
ronroy at ca.inter.net
Web page ronroy.net

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