[Clayart] Cracks and slow seepage- porcelain

paul gerhold gerholdclay at gmail.com
Sun Jul 11 20:27:17 UTC 2021


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


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