Janet H Walker on mon 29 mar 99
...still testing base glazes to find one that will allow my
oxides to run , but still let the glaze stay on the pot as well.
Hi Gracie.
I heard a presentation by Paul Lewing at NCECA about ways to
encourage glazes to intermingle. And it fits with a comment that
Ron Roy made on ClayArt some months ago.
Ron's comment was that "silica starved glazes are strongly
interactive." This leads me to wonder about the following
technique. Maybe try for two base glazes. One that is "normal" and
one that is low in silica and alumina. Put the colorants into the
"low" glaze and put the other glaze on top of it as a clear. See
what happens. If those oxides don't just swim around, maybe they
need special swimming lessons.
Any comments from the gurus?
Jan Walker
Cambridge MA USA
Paul Lewing on tue 30 mar 99
Janet H Walker wrote:
>
> ----------------------------Original message----------------------------
> ...still testing base glazes to find one that will allow my
> oxides to run , but still let the glaze stay on the pot as well.
>
> Hi Gracie.
>
> I heard a presentation by Paul Lewing at NCECA about ways to
> encourage glazes to intermingle. And it fits with a comment that
> Ron Roy made on ClayArt some months ago.
For those of you who were not at the presentation, here's what I said.
I am working on a hypothesis that seems to hold true for all the glazes
I've worked with so far. I was trying to see from the molecular
analysis what determined whether two glazes would run a long way into
each other when fired next to each other, and what glazes would just lay
there and not intermix. I expected it to have to do with low alumina,
but it seems to have more to do with low silica.
I find the percentage by weight number to be more indicative of a
glaze's performance than the molecular number for silica, and for two
glazes to really get "fuzzy" with each other, both need to have SiO2
less than 50% by weight (this is at cone 4). Then you look at the
SiO2:Al2O3 ratio. If there is a difference of at least 7 in the ratios,
e.g. one has a ratio of 5 and the other a ratio of 12, then they will
interact strongly. This means that they both need to be low in silica,
and one of them also needs to be low in alumina, but the other needs to
be high in alumina. Make sense? I'd appreciate it if those of you with
calculation programs would check this hypothesis out on the glazes you
know about and tell me if I'm right.
Paul Lewing, Seattle
gwalker on tue 30 mar 99
G'day Janet ... been meaning to reply to something you have written for
ages! (And hello Gracie!)
I am not sure here exactly what effect you are talking about, but it
seems to me that it might be the effect one gets from one glaze boiling
though another in the melt. This leaves "oil-spot" effects on the
surface.
To achieve these ffects, the technique you mentioned is ideal. However,
similar effects can be achieved by altering the glazes in other ways
too. The idea is to get the lower glaze to melt before the upper one.
(Didn't want to say under- and over-glaze.)
Particle size plays a role in the melt (a much larger role than I had
previously thought, I found to my dismay recently ... see archives), and
this phenomenon can be used to advantage. Use ingredients (like silica)
of a finer mesh in the lower glaze, and coarser in the upper. This can
even make a dull glaze interesting ... mix a recipe twice, one with each
particle size, and apply two coats ... the finer first ... more
interesting if more than one colourant is used. (Many variations on
this: eg. two glazes with the same formula, but a different colouring
oxide in each ... or NONE in one. Mix the one you want to be the lower
glaze with the finer particles etc.)
If you like to overlap glazes, do the same thing ... finer particles in
the lower glaze etc.
Of course, always test.
I hope this is of interest.
Clay hugs,
Geoff.
http://www.cronulla-pot.com.au/
Louis Katz on wed 31 mar 99
Hi Paul,
I am not sure if this would be of any help., but I have been predicting the
running of mixes of glazes in my classroom by comparing fluxes. Theory: If
the glazes contain different secondary fluxes in appreciable amounts they
tend to run.
Louis
Paul Lewing wrote:
> ----------------------------Original message----------------------------
> Janet H Walker wrote:
> >
> > ----------------------------Original message----------------------------
> > ...still testing base glazes to find one that will allow my
> > oxides to run , but still let the glaze stay on the pot as well.
> >
> > Hi Gracie.
> >
> > I heard a presentation by Paul Lewing at NCECA about ways to
> > encourage glazes to intermingle. And it fits with a comment that
> > Ron Roy made on ClayArt some months ago.
>
> For those of you who were not at the presentation, here's what I said.
> I am working on a hypothesis that seems to hold true for all the glazes
> I've worked with so far. I was trying to see from the molecular
> analysis what determined whether two glazes would run a long way into
> each other when fired next to each other, and what glazes would just lay
> there and not intermix. I expected it to have to do with low alumina,
> but it seems to have more to do with low silica.
> I find the percentage by weight number to be more indicative of a
> glaze's performance than the molecular number for silica, and for two
> glazes to really get "fuzzy" with each other, both need to have SiO2
> less than 50% by weight (this is at cone 4). Then you look at the
> SiO2:Al2O3 ratio. If there is a difference of at least 7 in the ratios,
> e.g. one has a ratio of 5 and the other a ratio of 12, then they will
> interact strongly. This means that they both need to be low in silica,
> and one of them also needs to be low in alumina, but the other needs to
> be high in alumina. Make sense? I'd appreciate it if those of you with
> calculation programs would check this hypothesis out on the glazes you
> know about and tell me if I'm right.
> Paul Lewing, Seattle
--
Louis Katz
lkatz@falcon.tamucc.edu
NCECA Director of Electronic Communication and Webmaster
Texas A&M-CC Division of Visual and Performing Arts
Visit the NCECA World Ceramics Image Database Online
Looking for a school or a class? Visit NCECA Ceramics Educational Programs
Database Online
Coastal Bend Arts Calendar Webmaster
Barney Adams on wed 31 mar 99
Hi,
I have a glaze combo that gives the feathering fairly regular. Unfortunately
I only have the formula for one the other was from a supplier. I can say
That my glaze has high silica and moderate alumina and usually needs
to be the lower glaze. The other glaze tends to be very runny and I assume
this would be low alumina. I wonder if the timing of the melt and viscosity
balance has a lot to do with this. The line between the glazes melt at
different
amounts allowing the two glazes to mix by various amounts along the line?
Barney
Paul Lewing wrote:
> ----------------------------Original message----------------------------
> Janet H Walker wrote:
> >
> > ----------------------------Original message----------------------------
> > ...still testing base glazes to find one that will allow my
> > oxides to run , but still let the glaze stay on the pot as well.
> >
> > Hi Gracie.
> >
> > I heard a presentation by Paul Lewing at NCECA about ways to
> > encourage glazes to intermingle. And it fits with a comment that
> > Ron Roy made on ClayArt some months ago.
>
> For those of you who were not at the presentation, here's what I said.
> I am working on a hypothesis that seems to hold true for all the glazes
> I've worked with so far. I was trying to see from the molecular
> analysis what determined whether two glazes would run a long way into
> each other when fired next to each other, and what glazes would just lay
> there and not intermix. I expected it to have to do with low alumina,
> but it seems to have more to do with low silica.
> I find the percentage by weight number to be more indicative of a
> glaze's performance than the molecular number for silica, and for two
> glazes to really get "fuzzy" with each other, both need to have SiO2
> less than 50% by weight (this is at cone 4). Then you look at the
> SiO2:Al2O3 ratio. If there is a difference of at least 7 in the ratios,
> e.g. one has a ratio of 5 and the other a ratio of 12, then they will
> interact strongly. This means that they both need to be low in silica,
> and one of them also needs to be low in alumina, but the other needs to
> be high in alumina. Make sense? I'd appreciate it if those of you with
> calculation programs would check this hypothesis out on the glazes you
> know about and tell me if I'm right.
> Paul Lewing, Seattle
Janet Price on wed 31 mar 99
I have had good luck with one glaze running into another by using the
following glaze under the one I want to run. I glaze the lower 2/3 of a
vase in one glaze, brush the glaze below on the top 1/3 of the vase and
then dip the top third in a different glaze. I use this on porcelain
clay and fire around cone 5. While it seems to work with almost all
glaze combinations I've tried, some are more interesting than others and
the pattern of runs is different for the different glaze combinations.
The glaze below began with Zakin's GK glaze.
36 frit 3124
14 magnesium carbonate
20 neph sye
22 strontium
30 spodumene
20 EPK
26 whiting
24 superpax
2 bentonite
30 unwashed wood ash from fireplace
Of course it could be the result of whatever kind of wood my friend used
in her fireplace. This glaze by itself is not particularly
interesting. You should watch for excessive runs, but I've seldom had
the glaze run off the pots.
--
Janet Price, Chief Information Officer
Carroll College, Waukesha WI 53186
jprice@carroll1.cc.edu or jprice@ccadmin.cc.edu
414-524-7120
DinaH on fri 9 apr 99
I tried to send this to Gracie but it didn't work
.Gracie
I think I understand what you're looking for---maybe.
Have you ever seen any Newcomb pottery? There were different
periods but the
one I really loved was when the glazes looked like you were
seeing them through
a mist. The oxides were kind of hazy.
I tried to duplicate that look on my own with no luck. I went to
ASU and took a
class in glaze calculation. I worked all semester trying to get
it. Didn't. I
talked to Pete Pinnell at NCECA in New Orleans and he suggested
I try his
Weathered Bronze without the colorants. I made up a wash of
cobalt oxide and
copper carb and painted this randomly over a bisqued piece. Then
I dipped it in
Pete's glaze (not too thick). Actually it was pretty
interesting--not Newcomb
but not bad.
The woman who taught the class sent me a note recently
suggesting I try Tony
Hansen's clear matt over oxides. I plan to try it. If its good
I'll let you
know.
Dinah
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