[Clayart] Microwave heating

[Paul Gerhold]

Your statement was that capillary action in fired clay will keep moisture in the clay indefinitely.  As far as I know fired clay has pores and not capillaries.  And yes, I am following the conversation which is why I question a clay theory based on the assumption that capillary action has any relevance to clay. 

And I also question the assumption that moisture once absorbed into clay will stay there indefinitely. My opinion is that the moisture in the pores will gradually equilibrate with the moisture content in the surrounding air.

Paul
Sent from my iPad

> On Nov 8, 2016, at 8:42 PM, John Hesselberth <jjhesselberth at gmail.com> wrote:
> 
> I’m talking about a fired piece that has some residual porosity. Are you following this conversation or just looking for places to take pot shots?
> 
> John
> 
> 
>> On Nov 8, 2016, at 6:51 PM, Paul Gerhold <gerholdclay at gmail.com> wrote:
>> 
>> John,
>> I would be interested in why you think capillary action has anything to do with wheel thrown ceramics.  
>> 
>> Paul
>> 
>> Sent from my iPad
>> 
>>> On Nov 8, 2016, at 12:08 PM, John Hesselberth <jjhesselberth at gmail.com> wrote:
>>> 
>>> Hi Paul,
>>> 
>>> I think you are misunderstanding what we are talking about. The water gets into the mug over a period of days, weeks, or months when the mug is soaking in the sink, in the dishwasher, or wherever the surface can get get. If not adequately vitrified, a tiny bit of water will work its way into the mug during those times. It stays there. Drying it with a towel will not draw it out. Capillary action will probably keep it there indefinitely even if it sits in a dry cabinet for a long time. It is that water which heats rapidly on microwaving.
>>> 
>>> Regards,
>>> 
>>> John
>>> 
>>>> On Nov 8, 2016, at 7:46 AM, Paul Gerhold <gerholdclay at gmail.com> wrote:
>>>> 
>>>> It is hard for me to imagine that if you take a dry mug , add water  and then microwave for a minute or two that enough water can be absorbed by the body to explain the heating.  Perhaps someone with a mug with this problem can weigh a mug, microwave it, remove the water, dry thoroughly and then reweigh to test the water absorption hypothesis.
>>>> 
>>>> Paul  
>>>> 
>>>> Sent from my iPad
>>>> 
>>>>> On Nov 7, 2016, at 8:10 PM, John Hesselberth <jjhesselberth at gmail.com> wrote:
>>>>> 
>>>>> Hi Everyone,
>>>>> 
>>>>> I have been asked off list to post my thoughts on how to assure your pots will not get scalding hot in a microwave.  I have found that getting the water absorption of your fired body down to 2% or less does the job. The procedure for testing that has been posted on the list by Ron Roy several times or it is in our book.  Or bug Ron to post it again—we have let him off kind of light recently.
>>>>> 
>>>>> There are one or two people on the list who say they have seen the overheating with glazes heavy in iron. I have not seen that with glazes containing up to 9% iron oxide (e.g. Licorice) but maybe it happens in rare circumstances. Clearly minimizing water absorption is the place to start. And don’t rely on the clay manufacturer’s numbers—test it yourself in your kiln firing at your normal conditions, It is pretty easy to do.
>>>>> 
>>>>> John
>>>>> 
>>>>> John Hesselberth
>>>>> john at frogpondpottery.com <mailto:john at frogpondpottery.com>
>>>>> 
>>>>> "I love everything that's old: old friends, old times, old manners, old books, old wines." Oliver Goldsmith, "She Stoops to Conquer" (1773)
>>>>> 
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