[Clayart] Wollastonite/hardening clay bodies

robert hackert ndiaman at hotmail.com
Wed Jul 19 21:00:06 EDT 2017


Hello Paul:
I concur with your comment. Wollastonite practically needs to be ball milled. The chunks will not dissolve without some vigorous screening. It does contribute silica to a glaze, but for me, I can do w/o it.

Robert Hackert

Sent from my iPhone

> On Jul 19, 2017, at 7:40 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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