Judy Smith on thu 13 jan 11
I'm looking for a matte glaze that is also a little runny. I like the runn=
y
when I layer 2 glazes. I fire my pottery at cone 6 oxidation. Is it
possible for a matte glaze to also be runny? All of my runny crystalline
glazes are glossy. If you have a recipe like this, I sure would appreciate
you letting me try it.
Thanks,
Judy Smith
Nashville, TN
Snail Scott on fri 14 jan 11
On Jan 13, 2011, at 10:32 AM, Judy Smith wrote:
> ... Is it
> possible for a matte glaze to also be runny? All of my runny crystalline
> glazes are glossy...
True matte glazes can easily be runny. The difference
between a true matte glaze and a false one is that
false mattes are merely underfired, and might well
be glossy if fired hot enough. A true matte glaze melts
just fine at its optimum temperature; the matteness
occurs during the cooling cycle as micro-crystals
form and make it look less shiny.
Your crystalline glazes (we'll call them macro-
crystalline for now, just to clarify) do something
very similar, but instead of the entire glaze forming
microcrystals all over, the crystals form around
isolated bits of stuff which act as starting points. The
crystals grow around those points, sucking all the
relevant minerals out of the surrounding glaze as
they grow. Thus, the surrounding glaze is indeed
really shiny. It's not shiny because it's runny, though.
It's shiny because it retains none of the materials that
crystallized out of the mix, and it's the runniness of
the glaze that allowed them to do that. Such large
crystals could never grow in a stiffer glaze.
If your favorite matte glazes aren't runny enough,
they may simply not be fully melted. They may be
matte merely because they are underfired glazes
labeled as matte, or they may be true matte but not
very runny. Try a longer hold at peak temperature.
This will give the glaze more time to melt and run
if it's inclined to do so. If this doesn't help much, try
adding a bit of extra flux to the mix. It will make a
true matte more runny, but may reveal a false matte
to be a higher-temp gloss glaze in disguise.
(Personally, if a so-called 'glaze' doesn't fully melt
at the temperature it's used at, I'd call it an engobe.)
-Snail
David Finkelnburg on fri 14 jan 11
Judy,
When I first made a glaze I wondered, too, if a glaze that was runny
could be matte. The answer is yes!
By now I imagine you've had plenty of input on this. The ingredients
which keep a glaze from being runny are the elements which link together an=
d
form the network--at your temperature mostly silica, aka silicon dioxide
(SiO2), and a "network modifier" which is alumina, Al2O3. All it takes to
make a glaze runny is to have it be deficient in either or both of these
materials. The more deficient in these, the runnier the glaze.
True matte glazes, ones that melt fully before crystals precipitate fro=
m
the melt to make the surface matte rather than glossy, do not have enough
glass former or network modifier to make the glaze glossy. Thus, true matte
glazes tend to be runny to begin with.
At cone 6 your glossy glazes will have a ratio of about 1 mole of fluxe=
s
(total) to 0.25 moles of alumina to 2.5 moles of silica. Clay contributes
alumina and silica to a glaze so using less of it will tend to make a glaze
runnier.
How thickly you apply the glaze, what else is in the recipe, the form
you glaze and your clay body are all variables that will influence how much
any glaze will run. Thus it's a good idea to test runniness carefully.
Firing on a shallow dish of your clay, a drip catcher, can save you from
ruining shelves while you explore runny glazes.
This is just scratching the surface of a really fun subject.
Good glazing,
Dave Finkelnburg
http://www.mattanddavesclays.com
-----------------------------
Date: Thu, 13 Jan 2011 10:32:18 -0600
From: Judy Smith
Subject: Both runny and matte?
I'm looking for a matte glaze that is also a little runny. I like the runn=
y
when I layer 2 glazes. I fire my pottery at cone 6 oxidation. Is it
possible for a matte glaze to also be runny? All of my runny crystalline
glazes are glossy. If you have a recipe like this, I sure would appreciate
you letting me try it.
=3D
Edouard Bastarache on fri 14 jan 11
Hello David,
check this out and see if it helps :
http://glazeexpansion.blogspot.com/Gis,
Edouard Bastarache
Spertesperantisto
Sorel-Tracy
Quebec
http://www.flickr.com/photos/30058682@N00/
http://edouardbastarache.blogspot.com/
http://www.facebook.com/edouard.bastarache
http://bastaracheblogsarts.blogspot.com/
----- Original Message -----
From: "David Finkelnburg"
To:
Sent: Friday, January 14, 2011 5:40 PM
Subject: Re: Both runny and matte?
> Judy,
> When I first made a glaze I wondered, too, if a glaze that was runny
> could be matte. The answer is yes!
> By now I imagine you've had plenty of input on this. The ingredients
> which keep a glaze from being runny are the elements which link together
> and
> form the network--at your temperature mostly silica, aka silicon dioxide
> (SiO2), and a "network modifier" which is alumina, Al2O3. All it takes t=
o
> make a glaze runny is to have it be deficient in either or both of these
> materials. The more deficient in these, the runnier the glaze.
> True matte glazes, ones that melt fully before crystals precipitate
> from
> the melt to make the surface matte rather than glossy, do not have enough
> glass former or network modifier to make the glaze glossy. Thus, true
> matte
> glazes tend to be runny to begin with.
> At cone 6 your glossy glazes will have a ratio of about 1 mole of
> fluxes
> (total) to 0.25 moles of alumina to 2.5 moles of silica. Clay contribute=
s
> alumina and silica to a glaze so using less of it will tend to make a
> glaze
> runnier.
> How thickly you apply the glaze, what else is in the recipe, the form
> you glaze and your clay body are all variables that will influence how
> much
> any glaze will run. Thus it's a good idea to test runniness carefully.
> Firing on a shallow dish of your clay, a drip catcher, can save you from
> ruining shelves while you explore runny glazes.
> This is just scratching the surface of a really fun subject.
> Good glazing,
> Dave Finkelnburg
> http://www.mattanddavesclays.com
>
> ------------------------------
>
> Date: Thu, 13 Jan 2011 10:32:18 -0600
> From: Judy Smith
> Subject: Both runny and matte?
> I'm looking for a matte glaze that is also a little runny. I like the
> runny
> when I layer 2 glazes. I fire my pottery at cone 6 oxidation. Is it
> possible for a matte glaze to also be runny? All of my runny crystalline
> glazes are glossy. If you have a recipe like this, I sure would
> appreciate
> you letting me try it.
> =3D
>
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