[Clayart] Cracks and slow seepage- porcelain

Antoinette Badenhorst porcelainbyantoinette at gmail.com
Mon Jul 12 15:41:28 UTC 2021


I had to reload the technofile about ^6 porcelain, since it came out messed
up. Here is the corrected link.
https://www.porcelainbyantoinette.com/uploads/4/7/7/2/47725299/2016-12_ceramics_monthly__better_porcelain_.pdf
Ric, I know you have a few wonderful videos about porcelain in China.
Please share again.

On Sun, Jul 11, 2021 at 6:43 PM Antoinette Badenhorst <
porcelainbyantoinette at gmail.com> wrote:

> It is often possible to fire cone 6 porcelain higher, since the flux used
> is sodium spar. As I understand it, sodium spar will only begin to flux at
> ^ 6 and mature at ^9.
>
> Almost all the dishes in my kitchen are porcelain these days. I do not
> cook every day as I used to do when my children was in the house, so we
> often eat microwaved leftovers. A bowl may get warm as heat is transferred
> into the clay walls, but the handles do not get hot.
>
> On the other hand , I cannot always say that about stoneware and
> earthenware.
> Every once in a while I will use a dish from either my own stoneware days,
> or one that I have from other potters and every once in a while the handle
> heats up. This happens
> when liquid seeps into the clay walls and heats up along with the food.
>
> I also have stoneware soap dispensers that I’ve been using for years. The
> soap seeps through the basis.
>
> Although there are many good things about firing to ^6, I also think that
> potters should not have a false reassurance about the clay they are using.
> As Ron pointed out, clay can vitrify over a range of temperatures.
>
> Also, good glazes are only good if it work on the clay body it is used
> for. There is a misconception about the temperature range of a clay body vs
> the clay that it is used on. For instance if a glaze works well on
> stoneware, it may run badly on porcelain.
> I just recently loaded this techno file on my website. It explains how I
> went ahead to create ^6 porcelain clay bodies, by mostly manipulating the
> fluxes.
>
> https://www.porcelainbyantoinette.com/uploads/4/7/7/2/47725299/technofile_cone_6_porcelain.pdf
>
>
> *PorcelainByAntoinette   <https://www.porcelainbyantoinette.com/#/>*
>
> *TeachinArt* <https://www.teachinart.com/antoinette-badenhorst.html>
>
> *International Academy of Ceramics*
> <https://www.aic-iac.org/en/member/antoinette-badenhorst/>
>
> *Mississippi Arts Commission*
> <https://arts.ms.gov/artist/antoinette-badenhorst/>
>
>
>
>
> On Jul 11, 2021, at 5:18 PM, paul gerhold <gerholdclay at gmail.com> wrote:
>
> Ron,
> I agree that it appears she is not actually firing to cone six. Miller #16
> has an absorption claimed by the manufactures as .12% plus or minus 1%.
> There may also be a glaze fit problem if the cracks are not through the pot.
>
> Not sure abot what that microwave test is supposed to show. Just tested
> three different empty functional  pots I have bought over the years and
> they all get hot after six ten second cycles in the microwave. Also one of
> the earthen ware clays I use to make personal functional pieces does the
> same thing at cone 6 and it has an absorption way below 1%.   I also just
> tested one that has never been used and even it got very hot.
>
> Paul
>
> Sent from my iPad
>
> On Jul 11, 2021, at 4:06 PM, ronroy at ca.inter.net wrote:
>
>
> Hi Madeleine,
>
>
> The clay is not vitrified enough and water etc. is getting in the clay
> over time. Does the description from Laguna say it's a cone 6 clay or does
> it say it is good over a range of temperatures?
>
>
> It's not uncommon for clay companies to sell clay that does not vitrify
> enough at the temperatures they specify. That means whats in the dish water
> and food also gets in.
>
>
> If you microwave one of the suspected pots and it gets hot it means there
> is water in it. Just microwave the empty pot 10 seconds at a time for 2
> minutes.
>
>
> I can send instructions on how to actually test the clay to see the
> percent of absorption.
>
>
> I hope you fire with cones - that is the only way you know you are getting
> to the temperature you want.
>
>
> Perhaps a call to Laguna would help. I would like to hear their
> explanation for one.
>
>
> RR
>
>
>
>
> Quoting Madeleine Hall-Arber <arber at mit.edu>:
>
>
> For years, I have thrown pots out of Miller/Laguna #16 clay fired to Cone
> 6 with slow cool, primarily using recipes from Mastering Cone 6 Glazes,
> though occasionally experimenting with other glazes?some from Britt?s
> compendium.  My daughter uses a variety of my small cups and bowls to
> prepare her meals in the microwave.  She never puts them in the dishwasher
> and handles them carefully.  We?ve noticed that several have developed long
> cracks that we can see (presumably from food stains).  In several cases,
> the foot of the pot has yellowed.  I?ve also noticed that our soap
> dispenser accumulates a scummy surface at the foot.  Any ideas?   I tell
> customers that my work can be used in the microwave (and dishwasher),
> should I not?
>
>
> Thanks for your help and knowledge!
>
> Madeleine
>
>
>
> Madeleine Hall-Arber
>
> Madeleine?s Mud Pie Studio
>
> (617) 510-5955
>
> Etsy: madmud.etsy.com
>
> Instagram: madeleinehallarber
>
>
>
>
>
>
>
>
>
>
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> Ron Roy
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> ronroy at ca.inter.net
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> Web page ronroy.net
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-- 

Best wishes,

Antoinette Badenhorst



*PorcelainByAntoinette   <https://www.porcelainbyantoinette.com/#/>*

*TeachinArt* <https://www.teachinart.com/antoinette-badenhorst.html>

*International Academy of Ceramics*
<https://www.aic-iac.org/en/member/antoinette-badenhorst/>

*Mississippi Arts Commission
<https://arts.ms.gov/artist/antoinette-badenhorst/>*
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