Jeff Jeff on sun 23 may 10
I'm getting back into glaze experimentation and just wondering if anyone
knows why overlapping glazes yields a different result than mixing two glaz=
es
together?
As well are there general rules regarding overlapping: i.e. fluid glazes
best under or slip glazes best over, kind of a thing? I have a limited budg=
et
and can't go wild but would like to explore more than before.
I used to think my textures look best under solid opaque glazes. I've since
realized that fluid, transparent glazes accentuate the textures in
unexpected, and more pleasant, ways.
Thanks
Jeff Longtin
Minneapolis
paul gerhold on mon 24 may 10
Jeff,
Overlapping glazes are often most interesting when the glazes have differen=
t
melting characteristics, Also variations in thickness come into play when
overlapping glazes.
One of the rules in working with overlapping glazes is to test and test and
test. It is also very important to mix the glazes exactly the same each
time if you want semi-reproducible results. All my glaze formulas specify
not only the amount of chemicals but also the amount of water and use or no=
n
use of CMC. Small batches work better as well since glaze consistency
changes as you use the glaze.
Paul
On Sun, May 23, 2010 at 2:42 PM, Jeff Jeff wrote:
> I'm getting back into glaze experimentation and just wondering if anyone
> knows why overlapping glazes yields a different result than mixing two
> glazes
> together?
>
> As well are there general rules regarding overlapping: i.e. fluid glazes
> best under or slip glazes best over, kind of a thing? I have a limited
> budget
> and can't go wild but would like to explore more than before.
>
> I used to think my textures look best under solid opaque glazes. I've sin=
ce
> realized that fluid, transparent glazes accentuate the textures in
> unexpected, and more pleasant, ways.
>
> Thanks
>
> Jeff Longtin
> Minneapolis
>
David Finkelnburg on mon 24 may 10
Jeff,
Runny glaze over or runny glaze under, that is the question! Great
question you ask, btw! Isn't it funny how most imponderables really are
great to consider? :-)
Seriously, layering is endlessly complicated. There are at least four
things at work, in my admittedly limited experience. First, which glaze
melts first? Second, how much do the two glazes interact? Third, what is
the viscosity of each glaze? That is not really a factor on flat tile
fired horizontally, btw. Fourth, what is the surface tension of each glaze=
?
Any person who wants to understand the possibilities should fire test
tiles of each of their glazes alone, over and under each of their other
glazes, and do this in different thicknesses, too. Then, of course, one ca=
n
also vary firing time (including cooling) and in the case of fuel-influence=
d
kilns, vary atmosphere.
You can see why with all these variables to work with layering may be a
challenge to fully understand. I like Paul Lewing's approach. He has said
for some time that the wider the variation between the
calculated silica:alumina ratio in two different glazes the more they will
interact and the more potentially interesting the result will be. As an
example, putting a 15:1 ratio (glossy) glaze on a tile and layering over
that with a 5:1 ratio (just barely matte) will produce strong interaction
according to Paul, and it does. Paul recommends a difference of at least 1=
0
in the Si:Al ratio .
I have found that glazes that don't interact much, but have different
surface tension (tendency to pull together) produce interesting effects if
the top glaze has a significantly higher surface tension. It will tend to
pull into islands on top of the other glaze.
If the top glaze melts first you can get crawling though most crawling
is produced by poor glaze adhesion to the ware. Dr. William Carty has
explained to me on several occasions that intentional crawling (crawling
glazes) require high surface tension in the glaze. Thus, one should use
caution when testing an exceptionally high surface tension glaze as the
bottom glaze. You may find the glaze falling onto the kiln shelves. :-(
Runny glazes don't do much on flat tile fired flat but on vertical ware
or on significant relief I find these personally most rewarding. Which to
put on first? There are no rules, no glaze layering police, it's more a
matter of preference and color and translucency, if any, of the different
glazes, and the effect you desire. My blue and green somewhat signature
(for my work) wood ash glazes capitalize on putting the runny glaze over an=
d
above, vertically, a glaze that doesn't move. It's entirely a choice, not =
a
rule or a suggestion.
Again, this is a fertile ground for testing. Please share your
experiences with your tests. Thanks!
Dave Finkelnburg in eastern Idaho where, like Kelly, the mud on m=
y
hands is not all clay. The spitting snow is frustrating, yet the soil was
warm to touch yesterday as I weeded the onions, spinach and peas. A farmer
friend tells me the corn is safe from the frost. "The growing point is
still under the ground so it will come back if it freezes," he observed as
we watched the snow waft by horizontally on Saturday and only the brave
bought pots or bedding plants...
http://www.mattanddavesclays.com
-----------------------------
Date: Sun, 23 May 2010 14:42:58 EDT
From: Jeff Jeff
Subject: Overlapping two glazes vs. mixing two glazes
I'm getting back into glaze experimentation and just wondering if anyone
knows why overlapping glazes yields a different result than mixing two
glazes
together?
As well are there general rules regarding overlapping: i.e. fluid glazes
best under or slip glazes best over, kind of a thing? I have a limited
budget
and can't go wild but would like to explore more than before.
I used to think my textures look best under solid opaque glazes. I've since
realized that fluid, transparent glazes accentuate the textures in
unexpected, and more pleasant, ways.
Thanks
Jeff Longtin
Minneapolis
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