[Clayart] Wollastonite/hardening clay bodies

Paul Gerhold gerholdclay at gmail.com
Fri Jul 7 16:46:25 EDT 2017


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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