McCoy, Jack on fri 3 jan 97
When I check my pottery supply catalogs for glaze materials
I see three different flints: 200, 325, and 400-mesh.
Which should I use for the glaze recipes passed around Clayart?
Thanks,
Jack
Ron Roy on sat 4 jan 97
>----------------------------Original message----------------------------
>When I check my pottery supply catalogs for glaze materials
>I see three different flints: 200, 325, and 400-mesh.
>
>Which should I use for the glaze recipes passed around Clayart?
>
>Thanks,
>Jack
Hi Jack,
As usual the answer starts with - it depends. The finer mesh materials are
easier to melt but I don't believe you can expect big differences. If you
are working at high temperature (cone 10) I don't believe you will notice
much difference but I have not done any experiments. Substituting finer
mesh materials at the lower temps (06 to 6) will probably give some
advantage to melting but again I don't have firsthand experience.
When choosing a mesh size for bodies - again it depends on what the problem
is. If you need more contraction from the Beta to Alpha quartz inversion to
counteract crazing then the larger mesh (200) will help more. If the
problem is the reverse - dunting - then more of the finer mesh silica will
be converted from crystaline (quartz) to amorphous silica and not go
through the inversion at 573C.
My personal choice would be the 200M simply because there will be less
airbourne particles to breath. I think adjusting the glaze to fit the clay
should be the first remedy tried - unless all the glazes are giving the
same trouble.
I guess we should ask those who post recipes to indicate the mesh size of
materials when appropriate.
Ron Roy
Toronto, Canada
Evenings, call 416 439 2621
Fax, 416 438 7849
Margaret Arial on sat 4 jan 97
'' IT HAS BEEN MY UNDERSTANDING THAT 200M IS ADEQUATE FOR STANDARD USE AND
PREFERABLE DUE TO THE HEALTH RISK INVOLVED BECAUSE THE FINER THE MESH THE
SMALLER THE PARTICLES WE BREATH AND SO ON.
David Hewitt on sun 5 jan 97
In message , "McCoy, Jack" writes
Hello Jack,
I am interested in your question as none of the catalogues I use in the
UK mention a mesh size for flint. Is this common in the US?
As to your question - which should I use - I have seen reference in Ian
Currie's book 'Stoneware Glazes - A Systematic Approach' that you need
silica of 200 mesh or finer. I would use the cheapest!
I look forward to reading some more informed replies.
Cheers,
>----------------------------Original message----------------------------
>When I check my pottery supply catalogs for glaze materials
>I see three different flints: 200, 325, and 400-mesh.
>
>Which should I use for the glaze recipes passed around Clayart?
>
>Thanks,
>Jack
>
David Hewitt
David Hewitt Pottery Caerleon, Tel:- 01633 420647
7 Fairfield Road, Caerleon, Newport, South Wales, UK.
URL http://digitalfire.com/magic/hewitt.htm
Robert Wilt on sun 5 jan 97
>When I check my pottery supply catalogs for glaze materials
>I see three different flints: 200, 325, and 400-mesh.
>
>Which should I use for the glaze recipes passed around Clayart?
To add to what Ron Roy said... At one studio where I work they use
325m silica, and I asked why. The reason they gave was that some
years ago they had done experiments with 200m vs. 325m silica in
the glazes, and found the 325m silica gave better results with
certain glazes - in particular, the transparent and translucent
glazes. Seems to make sense. These are cone 10 reduction glazes,
by the way.
bob
Frank Tucker on sun 5 jan 97
At 10:02 AM 1/4/97 EST, you wrote:
>----------------------------Original message----------------------------
>'' IT HAS BEEN MY UNDERSTANDING THAT 200M IS ADEQUATE FOR STANDARD USE AND
>PREFERABLE DUE TO THE HEALTH RISK INVOLVED BECAUSE THE FINER THE MESH THE
>SMALLER THE PARTICLES WE BREATH AND SO ON.
>
I would be careful with this line of thinking.I don't have the exact figures
with me here but a screen analysis of 200m. silica will show that about 96%
will go through a 400m. screen and 99% of 400m.silica will go through the
same screen.
Frank Tucker
Tucker's Pottery Supplies
HWCGmc1@aol.com on tue 7 jan 97
200 mesh flint sold today is finer than it used to be. Much of it passes
thru a 325 mesh screen. Grinding equipment at the processing plants is more
efficient. It is unlikely that 400mesh is necessary. I agree with Ron, 200
mesh is a good all around size.
Brian McCarthy
Highwater Clays
Ron Roy on tue 7 jan 97
David Hewitt wrote -
>Hello Jack,
>I am interested in your question as none of the catalogues I use in the
>UK mention a mesh size for flint. Is this common in the US?
>As to your question - which should I use - I have seen reference in Ian
>Currie's book 'Stoneware Glazes - A Systematic Approach' that you need
>silica of 200 mesh or finer. I would use the cheapest!
>I look forward to reading some more informed replies.
>Cheers,
There is a difference between Flint - a British material and what we use here.
We buy and use silica which is almost pure SiO2. Flint has about 4% Calcium
Carbonate (Hamer.)
Whats the point you say? Well I am wondering if the material purchased by
DH is Flint or Quartz and/or is the silica/quartz listed separately in his
catalogue?
Ron Roy
Toronto, Canada
Evenings, call 416 439 2621
Fax, 416 438 7849
David Hewitt on fri 10 jan 97
In message , Ron Roy writes
>
>There is a difference between Flint - a British material and what we use here.
>
>We buy and use silica which is almost pure SiO2. Flint has about 4% Calcium
>Carbonate (Hamer.)
>
>Whats the point you say? Well I am wondering if the material purchased by
>DH is Flint or Quartz and/or is the silica/quartz listed separately in his
>catalogue?
>
>Ron Roy
Flint and Quartz are always listed separately. Silica only as Silica
Sand for grog or placing. As you say, if I order Flint I would expect
some calcium carbonate.
The catalogues I refer to are Potclays, Potterycrafts and Bath Potters'
Supplies. None is a source supplier but are craft pottery suppliers. I
imagine if I went back to them I could get a more detailed
specification. Do you specify the mesh size of your flint or quartz or
silica?
David Hewitt
David Hewitt Pottery Caerleon, Tel:- 01633 420647
7 Fairfield Road, Caerleon, Newport, South Wales, UK.
URL http://digitalfire.com/magic/hewitt.htm
Ron Roy on sun 12 jan 97
>----------------------------Original message----------------------------
>In message, Ron Roy writes
>>
>>There is a difference between Flint - a British material and what we use here.
>>
>>We buy and use silica which is almost pure SiO2. Flint has about 4% Calcium
>>Carbonate (Hamer.)
>>
>>Whats the point you say? Well I am wondering if the material purchased by
>>DH is Flint or Quartz and/or is the silica/quartz listed separately in his
>>catalogue?
>>
>>Ron Roy
>Flint and Quartz are always listed separately. Silica only as Silica
>Sand for grog or placing. As you say, if I order Flint I would expect
>some calcium carbonate.
>The catalogues I refer to are Potclays, Potterycrafts and Bath Potters'
>Supplies. None is a source supplier but are craft pottery suppliers. I
>imagine if I went back to them I could get a more detailed
>specification. Do you specify the mesh size of your flint or quartz or
>silica?
>David Hewitt
The routine here is: If you order silica you get 200M @ $13.10 per 50 lb.
If you order 400M you get 400M @ $15.50 per 50 lb. As Frank Tucker points
out they are almost the same and I agree with David Hewitt why pay more? I
would still like to SEE the difference if any. Someone on the list said
they were told there was a difference but I cannot discern any at cone 10R.
Any difference would be more likely seen at faster firing and/or at lower
temperatures. Anybody have any hard info for us?
We are probably dealing with many suppliers of silica and perhaps different
mesh sizes - this information should be included in the safley data sheets
which every supplier must produce when asked.
Ron Roy
Toronto, Canada
Evenings, call 416 439 2621
Fax, 416 438 7849
Louis Katz on mon 13 jan 97
I have seen finer silica impact a cone six glaze. Mixing with finer silica
gets more of the silica dissolved and does seem to reduce crazing. Slow
firings might produce the same results.
I am still using coarse silica in my cone ten glazes, but if I was firing
faster I would at least think about changing to finer silica. The
diffences between slow and fast fired glazes can be very subtle, and I
suspect that the differences between fine and coarse silica in the
visual aspects of stoneware glazes would be subtle also.
A fast fired glaze can be like a slush of low viscosity glaze mixed with
unmelted sand and a slow fired glaze can be more homogenous with a more
viscose (lower temperature, higher viscosity) glaze and fewer undissolved
particles. Fast fired glazes seem to give muddier color.
Just some thoughts, make make sense to you before you believe no?
Louis
***************************************************
*Louis Katz lkatz@falcon.tamucc.edu *
*Texas A&M University Corpus Christi *
*6300 Ocean Drive, Art Department *
*Corpus Christi, Tx 78412 *
*Phone (512) 994-5987 *
**************************************************
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