William & Susan Schran User on tue 20 jun 06
Have started working with my students on saggar firing as part of our summer
raku course.
Have made some terra sig. according to Vince's instructions.
Will experiment with added colorants in the future,
but was wondering if anyone has tried adding an opacifier to the terra sig?
Would a zirconium silicate or tin oxide be a better choice?
I would probably add it after the terra sig. is made,
then ball mill the mix.
Thoughts?
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
Vince Pitelka on tue 20 jun 06
Bill Schran wrote:
> Will experiment with added colorants in the future,
> but was wondering if anyone has tried adding an opacifier to the terra
> sig?
> Would a zirconium silicate or tin oxide be a better choice?
> I would probably add it after the terra sig. is made,
> then ball mill the mix.
Bill -
I have achieved opacity with terra sig simply by adding enough layers, which
is usually necessary if you want to get a good shine, so I am not sure why
opacity is an issue. And actually, there are times when a thin translucent
patina of terra sig can be a wonderful thing.
I have always gone on the belief that one should never add any non-clay
materials to a terra sig unless there is a specific reason, because any
added non-plastics will diminish the shine and alter the texture, even if
you ball mill. I am interested in your reasons for wanting more opacity,
and if you try this, I'll certainly be interested in the results. My terra
sig method is just one approach that I worked out pretty thoroughly, but
there are of course a world of variations that I have never explored, so I
am always interested in other people's experiments.
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
Marcia Selsor on tue 20 jun 06
both Ball clay and kaolin make white terra sig. So why would you use
an opacifier?
Marcia Selsor
http://marciaselsor.com
On Jun 20, 2006, at 10:25 AM, William & Susan Schran User wrote:
> Have started working with my students on saggar firing as part of
> our summer
> raku course.
>
> Have made some terra sig. according to Vince's instructions.
>
> Will experiment with added colorants in the future,
> but was wondering if anyone has tried adding an opacifier to the
> terra sig?
>
> Would a zirconium silicate or tin oxide be a better choice?
>
> I would probably add it after the terra sig. is made,
> then ball mill the mix.
>
> Thoughts?
>
>
> -- William "Bill" Schran
> Fredericksburg, Virginia
> wschran@cox.net
> wschran@nvcc.edu
Vince Pitelka on wed 21 jun 06
> Using OM4 and Grolleg for our terra sig., we find the need to build up
> several layers to get an opaque coverage. Sometimes this results in areas
> chipping off - perhaps need to allow to dry longer between layers.
> So I was thinking of adding an opacifier.
Bill -
If you are going to experiment with an opacifier I'd use zircopax rather
than titanium dioxide, but I still question the reasoning. I wish I knew
more about how the Greeks achieved such crisp linear decoration, but I'll
bet that they were patient about applying multiple coats with very thin sig.
A properly made and applied terra sig should not chip at all, as long as you
are applying it to bone-dry ware and are applying it in multiple very thin
layers. In my experience, the application consistency should be no thicker
than 1.15 specific gravity. It is always tempting to mix a thicker sig to
get more opacity from less coats, but you have to realize that you are
dealing with a medium that has very little capacity for shrinkage once it is
dry on the surface, and if it is not well-adhered, it will chip or flake.
In order to adhere properly, it seems to require very thin coats. There's a
description of how I apply it in my article at
http://iweb.tntech.edu/wpitelka/professional/terra_sig.htm.
But once again, Bill, my tendency to avoid using an opacifier is mostly
because I am such a purist about terra sig. But I have no right to expect
other people to follow that example, and I encourage you to experiment with
the opacifier. I'll be interested in hearing about your results.
Good luck -
- Vince
Vince Pitelka
Appalachian Center for Craft, Tennessee Technological University
Smithville TN 37166, 615/597-6801 x111
vpitelka@dtccom.net, wpitelka@tntech.edu
http://iweb.tntech.edu/wpitelka/
http://www.tntech.edu/craftcenter/
William & Susan Schran User on wed 21 jun 06
On 6/20/06 4:31 PM, "Marcia Selsor" wrote:
> both Ball clay and kaolin make white terra sig. So why would you use
> an opacifier?
We used OM4 ball and Grolleg for the terra sigs.
The Grolleg is white, but to get it opague on the edges of forms it has to
go on rather thick which sometimes leads to chipping.
So I was thinking adding an opacifier might resolve this issue.
On darker clay bodies it takes several layers to get a non-streaked
coverage, again, the idea behind an opacifier.
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
William & Susan Schran User on wed 21 jun 06
On 6/20/06 3:28 PM, "Vince Pitelka" wrote:
> I have always gone on the belief that one should never add any non-clay
> materials to a terra sig unless there is a specific reason, because any
> added non-plastics will diminish the shine and alter the texture, even if
> you ball mill. I am interested in your reasons for wanting more opacity,
> and if you try this, I'll certainly be interested in the results.
Vince,
Using OM4 and Grolleg for our terra sig., we find the need to build up
several layers to get an opaque coverage. Sometimes this results in areas
chipping off - perhaps need to allow to dry longer between layers.
So I was thinking of adding an opacifier.
As I've thought about this some more, I thought also about using titanium
dioxide as it is used in latex paint for an opaque white.
Hmmmm, back to the lab.
-- William "Bill" Schran
Fredericksburg, Virginia
wschran@cox.net
wschran@nvcc.edu
Lynne Antone on wed 21 jun 06
Bill,
We have always had the best success with Vince's recipe for terra sig. We get the best colors and no chipping or bubbling off later on. I use 3-4 coats, Paul I think does about the same. Last night I was dipping some of my leaves twice and then one brushed coat to finish. That gave me the best coverage clear and over the edges.
I have seen a couple of potters who brush a white porcelain like slip over their pots while very wet (depends on your slip recipe and its formulation), then later putting the terra sig over this. One advantage is that the pot is very smooth and doesn't usually need sanding first, I hate that part.
Lynne Antone
I also just did additions of Mason Stains to the terra sig and brushed on the colors last night. Will post when I get the results. I am going to fire the tiles with ferric chloride in aluminum foil saggars as soon as I can get them bisqed and ready.
--
Beaver Creek Arts
Olympia WA
USA
-------------- Original message ----------------------
From: William & Susan Schran User
> On 6/20/06 4:31 PM, "Marcia Selsor" wrote:
>
> > both Ball clay and kaolin make white terra sig. So why would you use
> > an opacifier?
>
> We used OM4 ball and Grolleg for the terra sigs.
> The Grolleg is white, but to get it opague on the edges of forms it has to
> go on rather thick which sometimes leads to chipping.
> So I was thinking adding an opacifier might resolve this issue.
>
> On darker clay bodies it takes several layers to get a non-streaked
> coverage, again, the idea behind an opacifier.
Marcia Selsor on wed 21 jun 06
I usually use white ts on a white body and red on a red body. I see
your point.
Marcia Selsor
http://marciaselsor.com
On Jun 21, 2006, at 6:06 AM, William & Susan Schran User wrote:
> On 6/20/06 4:31 PM, "Marcia Selsor" wrote:
>
>> both Ball clay and kaolin make white terra sig. So why would you use
>> an opacifier?
>
> We used OM4 ball and Grolleg for the terra sigs.
> The Grolleg is white, but to get it opague on the edges of forms it
> has to
> go on rather thick which sometimes leads to chipping.
> So I was thinking adding an opacifier might resolve this issue.
>
> On darker clay bodies it takes several layers to get a non-streaked
> coverage, again, the idea behind an opacifier.
>
>
> -- William "Bill" Schran
> Fredericksburg, Virginia
> wschran@cox.net
> wschran@nvcc.edu
Marcia Selsor
http://marciaselsor.com
Elizabeth Herod on thu 22 jun 06
Bill--
I used to work in a studio that had no white stoneware. I could not throw
porcelain. I experimented with various terra sigs, and consulted with Vinc=
e
and Marcia.
I put terra sig on everything, so that I was starting with a white base. M=
y
preferred recipe ended up being 70% EPK, 30% OM4 and sodium silicate. I pu=
t
this in the rock polisher with marbles for 24 hours, then poured it into a
glass jar, where it sat, and I followed Vince=B9s directions. The specific
gravity of the Sig was between 1.1 and 1.2. I measured by weighing, not
with a hydrometer.
I put the pot, bone dry on a banding wheel, and applied many coats, quickly=
.
You can generally see your coverage, and if there is a need to do more to
cover the color of the clay. I had great success with this, (thank you
Vince). My friends who did not want to take the time to put on all the
layers, (and they were better than I using white clay bodies to start), use=
d
a different recipe, and put on one or two layers. Their Sig was also
thicker than mine. They had trouble with it popping off and chipping.
I also do not use a dripping brush. Generally I gently tap off the excess.
IMHO you have to experiment. No two people apply glazes or slips in the
same way.
Best
Beth
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