[Clayart] Microwave heating

[Paul Gerhold]

Ron,
I understand that but if you have a mug say with an absorption rate of say 4% and it sits in an atmosphere that is say thirty percent humidity will the 4% void space in the mug be 100% moisture or will it equilibrate with the atmosphere and the 4% void be only 30% water.

My guess would be that the partial pressures of water will be equalized and the void space in the mug will be only 30% water.

Paul

Sent from my iPad

> On Nov 8, 2016, at 11:36 AM, ronroy at ca.inter.net wrote:
> 
> Hi Paul,
> 
> A not properly vitrified mug would be OK just out of the kiln - because there was not enough time for water to get into the clay.
> 
> Depending how vitrified the clay is it may take weeks of constant use and washing for the water to get into the clay - even faster if the glaze is crazed. Even moisture from the air will gradually get in.
> 
> RR
> 
> Quoting Paul Gerhold <gerholdclay at gmail.com>:
> 
>> 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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>> 
>> 
> 
> 
> 
> Ron Roy
> ronroy at ca.inter.net
> Web page ronroy.net
> 
>