Michael McDowell on mon 28 apr 97
Roger Bourland wrote asking for sources of Mt. St. Helens volcanic ash. It
will be the eighteenth anniversary of the big eruption of Mt. Saint Helens
this coming May 18th I believe. Most of the good sources have been long
buried now. My source for MSH ash was a parking lot just east of
Ritzville, WA, about 60 miles east of Moses Lake. I wrote an article for
Ceramics Monthly that appeared in Jan. 81 issue on the subject of Mt. St.
Helens ash as a glaze material. Indeed I was surprised to find that article
cited more than once in Mimi Obstler's fine book.
I believe that Seattle Pottery Supply (phone 1-800-522-1975) still has some
in inventory. It is listed in their catalog as "sized & screened", and they
are asking $6.50 US for five pounds. I've never used any of the ash from
Seattle Pottery Supply though, so I can't tell you just how suitable it is.
As I recall, their source was from Moses Lake, WA. I found that Moses Lake
deposits were still a little "grainy" for my taste. Sources just another 50
to a hundred miles further east, away from the volcano were a much finer
powder. I have no idea how effective the sizing & screening efforts of SPS
are in dealing with this. If you get MSH from Seattle Pottery Supply & find
it too grainy, you can try ball milling it a bit, that will work fine. The
larger particles, though still small enough to pass a 100 mesh dry
screening, will have a strong tendency to settle out of a glaze slurry,
even when care is given to including suspending agents in the batch.
One solution I have found most useful short of ball milling is to
"pre-settle" the volcanic ash by mixing it up thin with water & then
pouring off what doesn't settle out in about a minute. Settle this
remainder more slowly. Pour or siphon off the clear water and you'll have
what I label MSH FFF in my studio, a much more practical ingredient, save
for its expense. The coarser remainder still has its uses, some potters I
know use it as an ingredient in their claybody. I consider it an excellent
garden soil ammendment, a great source of plant micro-nutrients. Farmers
around Ritzville mostly dry farm winter wheat, and there was lots of
complaining at first about all the extra wear this fine abrasive was going
to cause on the farm equipment. Then they had to give the ash the credit
for several successive years of bumper harvests, literally overflowing
their storage silos!
Michael McDowell
Whatcom County, WA USA
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