Dave Finkelnburg on thu 16 dec 99
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
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