John Hesselberth on thu 16 dec 99
This is a great suggestion from Dave. I'll incorporate it into my
instruction set that is on my site--and change my own cup size to match
this for future samples. Please consider doing it on your samples.
While it won't make us perfectly cross comparable, it is a significant
step in the right direction. John
Dave Finkelnburg wrote:
>
>>To those who are interested in testing glazes for leaching:
>> Would you like to get even more information from glaze leach testing?
>>Making your sample containers about the same size could help do that.
>>Here's why.
>> Right now leach testing is done using any "small" container you choose.
>>Depending on the container's shape and its dimensions, the area actually
>>exposed to the leach solution can vary quite a bit.
>> As I understand it, the test is to put a fixed quantity of leaching
>>solution into the container for a certain number of hours, and then analyze
>>the solution to see what, if anything, it has managed to leach from the
>>glaze. The analysis measures the weight of chemical leached per unit
>volume
>>of the solution.
>> It stands to reason that if the container used is a perfect hemisphere
>>just large enough to hold the solution, then the surface area actually
>>leached is a minimum. However, if the container is either tall and narrow
>>or wide and shallow, more surface area gets leached for the same volume.
>>Then the results can vary quite a bit, not because of any difference in the
>>glaze, but just because of the container shape.
>> To reduce this variation, I suggest that those who test their glazes
>for
>>leaching consider making test containers the same size, say simple
>cylinders
>>like water glasses, 4-inches inside diameter by at least 3-inches high
>(when
>>freshly thrown). They'll shrink, of course, but most functional pottery
>>will shrink a reasonably similar amount. The attempt here is not to make
>an
>>exact standard, but simply something that's easy to remember and to do.
>> Please keep in mind this would never be a requirement. However, if one
>>made containers of this size, the test results would be more comparable to
>>other leaching tests.
>> Since John Hesselberth really has pushed glaze testing so well, I have
>>already contacted him off-list for his opinion about this. He supports the
>>idea, and wrote, " I've been trying to do that for my own samples." He
>also
>>wants a size, "...easy...for anyone to throw."
>> If you have ideas or suggestions to improve on this, please do comment.
>>In the meantime, this is only a suggestion, not a requirement.
>> Good potting!
>> Dave Finkelnburg
>> dfinkeln@cyberhighway.net
John Hesselberth
Frog Pond Pottery
P.O. Box 88
Pocopson, PA 19366 USA
EMail: john@frogpondpottery.com web site: http://www.frogpondpottery.com
"It is time for potters to claim their proper field. Pottery in its pure
form relies neither on sculptural additions nor on pictorial decorations.
but on the counterpoint of form, design, colour, texture and the quality
of the material, all directed to a function." Michael Cardew in "Pioneer
Pottery"
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