Fonda Hancock on mon 16 may 05
I sent my ever patient husband to Nashville for chemicals from Mid-South
Ceramic and I have a dilemma. I have never gotten cornwall stone before,
but I have gotten wollastonite at least 5 times. The first time I bought
wollastonite, it was without lumps. The second time, and every other time
since that first time, it had large and small lumps that were really quite
hard and a pain to mix and get through the sieve. I even posted a question
here about that and got several replies that indeed wollastonite was often
lumpy. Now I take care of most of the lumps before I weigh and mix it. So
my dilemma is that I have two 5lb. bags, one marked wollastonite that is
very very smooth and more of an off-white color than in the past and one
marked cornwall stone, that I swear looks EXACTLY like my last 3 five lb.
batches of wollastonite; very white and very lumpy. My husband called Mid-
South with the dilemma and they assured him that both substances could be
lumpy or smooth depending on a number of things including the part of the
bag the material was taken; lumpy at the top and smooth at the bottom. So
now I don't know whether to mix a glaze according to what the labels say
they are or to go with what I think. Any ideas would be appreciated.
Fonda in Tennessee
Earl Brunner on mon 16 may 05
Cornwall can and often is lumpy.
Fonda Hancock wrote:I sent my ever patient husband to Nashville for chemicals from Mid-South
Ceramic and I have a dilemma. I have never gotten cornwall stone before,
but I have gotten wollastonite at least 5 times. The first time I bought
wollastonite, it was without lumps. The second time, and every other time
since that first time, it had large and small lumps that were really quite
hard and a pain to mix and get through the sieve. I even posted a question
here about that and got several replies that indeed wollastonite was often
lumpy. Now I take care of most of the lumps before I weigh and mix it. So
my dilemma is that I have two 5lb. bags, one marked wollastonite that is
very very smooth and more of an off-white color than in the past and one
marked cornwall stone, that I swear looks EXACTLY like my last 3 five lb.
batches of wollastonite; very white and very lumpy. My husband called Mid-
South with the dilemma and they assured him that both substances could be
lumpy or smooth depending on a number of things including the part of the
bag the material was taken; lumpy at the top and smooth at the bottom. So
now I don't know whether to mix a glaze according to what the labels say
they are or to go with what I think. Any ideas would be appreciated.
Fonda in Tennessee
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Earl Brunner
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Steve Irvine on mon 16 may 05
Fonda,
Cornwall Stone is a variable material and is sometimes an off white, but it can also be quite bluish.
It is often lumpy as it seems to absorb moisture from the air. The main thing to do if you are not
sure about whether you've got cornwall stone or wollastonite is to do a fusion test of samples in
your next firing.
Just put a thimble full of each questionable material on a tile and label them "mystery bag 1"
"mystery bag 2" etc. and fire them to glaze temperature. Cornwall stone on its own will begin to
melt at stoneware temperatures, but wollastonite is more refractory by itself and will look more
powdery.
Steve Irvine
http://www.steveirvine.com
Darlene Yarnetsky-Mudcat Pottery on tue 17 may 05
I agree cornwall stone can be very lumpy as well! Do you have a small
amount of each material left from previous batches that you could
test with? You might fire a small amount of each of the known
batches (in powder form) in small bowls then take a small amount of
each of the 2 unknown batches in small bowls and compare the
results. Just a thought.
Darlene Y.
Madison, IN
Fonda Hancock on sat 21 may 05
Steve, Thanks so much for the tip. I fired yesterday and tried your
suggestion and sure enough the stuff labled cornwall did melt and the
stuff labled wolla was way more powdery. I was dead wrong and you helped
me immensely. I need to weigh in with all those who post the praises of
this list. I lurk through the philosophical stuff and have started reading
the book, Art and Fear mentioned more than once. It is a truly wondrful
and affirming book. But the nitty gritty nuts and bolts stuff I find on
this list is what keeps me returning. Thanks Steve, Thanks Mel, Thank you
all who generously give of you time and knowledge. I love Clayart!
Fonda in Tennessee
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