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clay mixing problems

updated mon 31 mar 97

 

Jon Pettyjohn on wed 19 mar 97

Hi

I recently found a supplier here in Manila willing to
custom mix clay for me in 1 ton batches. This supplier
has been making casting clays for some local factories
but has no experience making hand-working bodies. The
clays they prepare are ball milled and filter pressed.

I asked them to add 5% 4o mesh silca sand for grog
but when the clay was finished we discovered that
this silica grog was not mixed well, it formed a
separate layer in the middle of each filter press cake
that is relatively dry and unmixed, I'm finding it
almost impossible to mix it back in and I'm afraid the
little clumps of dry silica will cause spalls in the
finshed pots.

Does anyone know how and when to add grog to ball-milled
filter-pressed bodies? The supplier has agreed to replace
the clay but I'm wondering how to correct this problem
for future batches.

Also I find the clay processed in this way is very
different from the same mixture I've been hand mixing
for many years, it's extremely smooth from the milling
but seems denser and less plastic.

any advice appreciated,

Jon Pettyjohn Manila jon@mozcom.com