Lawrence Carter on sat 7 nov 98
Crystalline glaze- crystal formation
I use the following base glaze; proportions by weight
Potclays Frit 2266 45
Calcined Zinc Oxide ( 1000 Deg C) 25
Flint 20
Titanium Dioxide 8
Calcined China Clay 0.5
Alumina Hydrate 0.5
Bentonite 1.0
The above is wet mixed, then ball milled for four hours. My batch weight
is made up to 3 kilos dry weight added to approx 2.5 kilos of clean
water. After ball milling the total weight of wet glaze is equally
divided into six parts, normally by weight.
For the calculation of the addition of various oxides it is assumed to
be based on 500 grams of dry material for each test, that is 3000
divided by 6. NB The actual weight of the wet mix is in the region of
850 to 900 grams due to losses in the ball milling or final seiving.
In order to minimise the variables involved I use one base glaze as
above, by the addition of small quantities of oxides from 0.01 to 5 %
to each test batch,based on the 500 gram dry wet. I reason that
providing I repeat this procedure my results are fairly consistent yet
not precise.
Oxides used so far;
manganese dioxide, manganese carbonate, lithium carbonate, cobalt oxide,
cobalt carbonate, copper carbonate, Red Iron Oxide, Titanium Dioxide,
Barium Carbonate, Molybdenum.
FIRING. 140 Deg C per hr up to 900
185 Deg C per hr up to 1280 switch off the power
I carefully open top loading electric kiln to crash cool to 1100 deg
Soak at 1100 degs for 3 hours crash cool in increments of 30 deg C for
90 minutes , 60 minutes, 20 minutes-- turn off at 1000 degs and allow to
cool naturally.
QUESTIONS
a) Is there a practical and reliable means to determine the actual melt
point of the glaze I use ? In order to decide the optimum temperature to
soak at to achieve large single crystals rather than many small
crystals.
b) Are there any high temperature coloured glaze stains available that
do not inhibit crystal growth.
c) Has anyone experience of using Molybdenum in very small quaintities,
up to 3% by weight and does this volatalise in the kiln at high
temperature.
I generally use a good quality porcelain which I bisque to 1000 Deg
C,after bisque firing I carefully rub down the pieces with 420 wet and
dry using soap and clean water.I thoroughly wash the pieces, generally
small bottle forms. These are thoroughly dried before a generous
application of glaze to the top two thirds of the pot. The pots are
mounted on pedestals placed in suitably deep saucers prior to firing, as
is standard practice I believe.
Your comments please, I would like to produce well differentiated
crystals witha distinct background rather than several small crystals.
Ball milling the glaze can reduce the melt temperature by about 20
degrees C. I have no idea what the actual temperature range is for the
crystalline growth, I assume it is somewhere between 1020 and 1100 deg C
but have no method of arriving at the real answer to this riddle.
Good luck from
a Crazy Crystalline Glazer.
--
Lawrence Carter
Louis on fri 27 nov 98
Hi Lawrence,
From reading your messages here goes:
A) The only reliable way I know of is to test at each temperature or cone
and decide which you like best. I would suggest: lower your firing cone
from cone 9 (1280 deg C) to cone 6 (1222 C). This should keep your glaze on
your pots and out of the dish. All the "experts" that do crystal glazes
that I have read and talked to, recommend that the crystal glaze be fired to
it's "maturing" cone, allowed to cool to a range of 2000 to 2100 deg F (1100
to 1160 C) and held there for one to four hours. The crystals grow at this
point. No one has ever said to "force" cool the kiln to the soaking temp,
and I have not tried it.
B) I don't know, you'll have to test the ones you are interested in. I
haven't come across any information on stains in crystal glazes.
C) I still haven't used my molybdenum in my own tests, but the information
available says that it volatilizes in the kiln and jumps around in the
kiln. The molybdenum crystals are supposed to be really nice.
I highly recommend you read Glazes for Special Effects by Herbert Sanders
and the new crystal glaze book that just became available. The best way I
have found to do tests is on the inside of small bowls, it saves time.
Good Luck,
Louis
Lawrence Carter wrote:
> ----------------------------Original message----------------------------
> Crystalline glaze- crystal formation
> I use the following base glaze; proportions by weight
> Potclays Frit 2266 45
> Calcined Zinc Oxide ( 1000 Deg C) 25
> Flint 20
> Titanium Dioxide 8
> Calcined China Clay 0.5
> Alumina Hydrate 0.5
> Bentonite 1.0
> The above is wet mixed, then ball milled for four hours. My batch weight
> is made up to 3 kilos dry weight added to approx 2.5 kilos of clean
> water. After ball milling the total weight of wet glaze is equally
> divided into six parts, normally by weight.
> For the calculation of the addition of various oxides it is assumed to
> be based on 500 grams of dry material for each test, that is 3000
> divided by 6. NB The actual weight of the wet mix is in the region of
> 850 to 900 grams due to losses in the ball milling or final seiving.
> In order to minimise the variables involved I use one base glaze as
> above, by the addition of small quantities of oxides from 0.01 to 5 %
> to each test batch,based on the 500 gram dry wet. I reason that
> providing I repeat this procedure my results are fairly consistent yet
> not precise.
> Oxides used so far;
> manganese dioxide, manganese carbonate, lithium carbonate, cobalt oxide,
> cobalt carbonate, copper carbonate, Red Iron Oxide, Titanium Dioxide,
> Barium Carbonate, Molybdenum.
> FIRING. 140 Deg C per hr up to 900
> 185 Deg C per hr up to 1280 switch off the power
> I carefully open top loading electric kiln to crash cool to 1100 deg
> Soak at 1100 degs for 3 hours crash cool in increments of 30 deg C for
> 90 minutes , 60 minutes, 20 minutes-- turn off at 1000 degs and allow to
> cool naturally.
> QUESTIONS
>
> a) Is there a practical and reliable means to determine the actual melt
> point of the glaze I use ? In order to decide the optimum temperature to
> soak at to achieve large single crystals rather than many small
> crystals.
>
> b) Are there any high temperature coloured glaze stains available that
> do not inhibit crystal growth.
>
> c) Has anyone experience of using Molybdenum in very small quaintities,
> up to 3% by weight and does this volatalise in the kiln at high
> temperature.
>
> I generally use a good quality porcelain which I bisque to 1000 Deg
> C,after bisque firing I carefully rub down the pieces with 420 wet and
> dry using soap and clean water.I thoroughly wash the pieces, generally
> small bottle forms. These are thoroughly dried before a generous
> application of glaze to the top two thirds of the pot. The pots are
> mounted on pedestals placed in suitably deep saucers prior to firing, as
> is standard practice I believe.
>
> Your comments please, I would like to produce well differentiated
> crystals witha distinct background rather than several small crystals.
> Ball milling the glaze can reduce the melt temperature by about 20
> degrees C. I have no idea what the actual temperature range is for the
> crystalline growth, I assume it is somewhere between 1020 and 1100 deg C
> but have no method of arriving at the real answer to this riddle.
>
> Good luck from
> a Crazy Crystalline Glazer.
>
> --
> Lawrence Carter
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