Lili Krakowski on thu 23 dec 04
At my age one of the accusations one gets is "You already TOLD me that =
story" and asides ( "The poor old dear is starting to reapeat herself... =
".) This makes Clayart so refreshing. One is INVITED to repeat =
oneself. Instead of feeling like a bore, one gets to feel like a GOOD =
person. ( I did this whole thing two days ago!)
I will leave it to Mr Lewis and others to give you the science. BUT =
some glaze materials dive to the bottom of the bucket and turn to rock, =
while others swim around and play. Fine. A lot of clay in the glaze =
prevents the clunking, but I mean quite a bit, and little or no Early =
Settlers.
What one does is add 2-3% Bentonite to the glaze as it is mixed, and =
add-a-few-drops-at-a-time of deflocculant in the slop. As Fraser (yes, =
THAT Fraser again) writes:
"Very often a combination of a few drops of calcium chloride and 2-3% of =
bentonite is added to the glaze. The calcium chloride, beiong a =
flocculant, make the galsze settle moare quickly, and also because of =
the larger flocks which are formed, makes the glaze more creamy and =
easier to work with. The bentonite counteracts the increased rate of =
settling, however, and so the combination of flocculant plust suspender =
results in a creamy glaze which is pleasant to ujse and works well yet =
does not settle too quickly."
Calcium chloride is sold in hardware stores to melt ice on the sidewalk. =
Unless you use it anyway there is little point in buying a 25 lb =
bucket. Epsom salts do the same thing and do NOT corrode metal. Get =
the cheaper Epsom salts (Magnesium sulphate) sold for bathing not =
injesting.
CLUE: If you automatically add this combo of bentonite and Epsom salts =
or Calcium chloride to your glazes--except the high clay ones, you will =
be infinitely happier in 2005.
Lili Krakowski
Be of good courage
Ivor and Olive Lewis on tue 28 dec 04
<some glaze materials dive to the bottom of the bucket and turn to
rock, while others swim around and play. >>
Dear Lili,
You are right, some minerals will dive to the bottom and need constant
agitation but, knowing that, it is just a small chore to give a stir
with Mel's 2 by 4. I have not used these chemical additives (Calcium
Chloride and Bentonite) because I seem to have glazes that dry out
before they get chance to settle. But I am concerned about what is
said of the reactions they cause.
A long time ago, when I had a palette for the stuff, we made home brew
beer, mead and wine.The instructions said that to get rid of the
excess cloudiness in the liquor you had to "fine it". To do this you
mixed up a paste of Bentonite and stirred it into the brew then let it
stand. The physics said that dense bentonite would slowly sink through
the liquid attracting yeast cells to it causing the wine or beer to
"Clear" leaving a mud sediment at the bottom of the jar.
Now it seems to me that Mr Fraser is telling us that the opposite
thing happens.
In one case bentonite causes sinking, in the other suspension.
One of the least understood concepts in ceramics is that of "The
Floc". Have you ever seen one? Has anyone got photographs of these
things? Are they present in ordinary plastic clay? What evidence is
there to say that there are big flocs and small flocs? How do we
recognise these things? How big are they? Do you need a microscope to
view them? I would suggest, if we do not know the material nature of a
floc, how do we manage to deflocculate and flocculate. Perhaps "Flocs"
are imaginary constructs which serve as useful models to explain the
behaviour of mineral suspensions.
Wishing you a Happy and Healthy New Year.
Best regards,
Mr Lewis.
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