Vince Pitelka on mon 3 oct 05
> My problem is as follows. I have made paperclay using BMIX cone 6. On my
> test tiles my terra sigillata layered in different colours and cut through
> to the under layers of different colours has fired well and looks great.
> BUT
> when I tried the same technique on 3-D forms it flaked off. I am only
> firing these to Bisque 04.
Joan -
I am curious as to what you are calling a terra sig. If it is a true terra
sig and is mixed too thickly, that would certainly contribute to flaking. A
true terra simply will not stand up to thick application. The particles are
so fine, and that contributes to high shrinkage, and thus the flaking and
peeling. Sanding should help it stick better, so that couldn't be the
cause. At what stage are you applying the terra sig? Normally, terra sig
is applied to dry greenware in extremely thin layers, and that doesn't seem
appropriate for most layered slip effects. If you specifically want a
layered slip effect, where you cut, carve, scrape, or sand through the
layers to expose successive colors, why would you even be using terra sigs?
Why not standard slips applied to the leather-hard greenware?
If you give me a little more information I might be able to help you. I am
a bit of a fanatic about how terra sigs are made, as you can see from my
terra sig article at
http://iweb.tntech.edu/wpitelka/professional/terra_sig.htm
Best wishes -
- 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/
Joan Conklin on mon 3 oct 05
Dear Friends,
I need some technical assistance. I am working in terra sigillata.
My problem is as follows. I have made paperclay using BMIX cone 6. On my
test tiles my terra sigillata layered in different colours and cut through
to the under layers of different colours has fired well and looks great. BUT
when I tried the same technique on 3-D forms it flaked off. I am only
firing these to Bisque 04.
Can anyone help with me this one?
I have tested the terra sig in layers on plain earthenware, plain B MIX and
on Paperclay B MIX with no problems. The test tiles are not covered with the
terra sig on the back. While the sculpture forms test had the terra sig all
around...covering the entire 3D form.
One other thing....the tiles were extruded....while the forms were hand
built and to finish them I did do some sanding. All those little joins to
get them perfect.
I look forward to hearing from you. Joan in Canada
Joan Conklin on tue 4 oct 05
Thank you Vince for replying to my call for help.
Yes, I followed your process. I love the look. It is a true terra sigillata.
I am quite good now at sucking the clay into my mouth before getting the
hang of siphoning. I even set my alarm clock at night so I would get the
time exactly correct. I made a white using Ball Clay, also used Red Art
Clay. Then I took commerical clay Midnight (black clay) and ran it through
the process and came up with a deep brown black (polishes to a deep brown)
and a Gold Stone Clay that come up to a rich orange gold. I also tested P300
which is a white porcelain but it was dusty. All the commerical clays tested
were cone 6 clays. All of the successful terra sigillata's produced a nice
soft satin shine on the BMix and on a Earthenware clay. They maintained the
shine to cone 6 temperatures but I decided in the initial tests that firing
them to earthenware temperatures was the best look...if not just to cone 04.
The problem started with the 3D application of multiple layers of terra
sigillata's all different colours layered and then cutting through to the
different coloured layers (looks great). I don't really intend to glaze any
of these pieces that is why I was using the terra sigillata rather than
slips.
I have had success in layering(layers of different colours of terra
sigillata) on the 2x4 inch test tiles but when I went to 3D forms I had
cracking and flaking. I may just be applying it in thicker coats on the 3D
forms. But I am beginning to think that if I want the colours to come
through I might be better to use slips under the terra sigillata.
I have never done anything like this before....so it is very experimental
for me. But the idea was to produce sculptures with repeat patterns created
by cutting throught the layers with the top surface being terra sigillata.
I was using the terra sigillata because I really had no plans on glazing any
of these pieces or if I did apply glaze it would be to make a glaze pattern
on top of the other patterns. I only have access to an electric kiln so I
couldn't produce the nice look of pit fired or smoked pots.
I really am open to any suggestions on how I could get this to work....or if
I need to switch processes in some way then I will. I did try one tile with
slip under the terra sigillata(one layer of terra sigillata) and then cut
through to overlapped layers of coloured slips and it was quite nice but
where the slip showed around the terra sigillata decorative motif I had this
.....clay look rather than the finished look for the terra sigillata. I also
tried sponge decorations of terra sigillata decoration and that was quite a
nice effect.
Ah yes when I tried glazing some of my test tiles what happened was the
colours in the red art clay, and the midnight brown/black just got washed
out. Seems a shame to make terra sigillata and then glaze over it.
Thank you for any help you can give me. Kind Regards, Joan
>From: Vince Pitelka
>Reply-To: Clayart
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Re: Terra Sigillata Application Problem
>Date: Mon, 3 Oct 2005 22:41:24 -0500
>
>>My problem is as follows. I have made paperclay using BMIX cone 6. On my
>>test tiles my terra sigillata layered in different colours and cut through
>>to the under layers of different colours has fired well and looks great.
>>BUT
>>when I tried the same technique on 3-D forms it flaked off. I am only
>>firing these to Bisque 04.
>
>Joan -
>I am curious as to what you are calling a terra sig. If it is a true terra
>sig and is mixed too thickly, that would certainly contribute to flaking.
>A
>true terra simply will not stand up to thick application. The particles
>are
>so fine, and that contributes to high shrinkage, and thus the flaking and
>peeling. Sanding should help it stick better, so that couldn't be the
>cause. At what stage are you applying the terra sig? Normally, terra sig
>is applied to dry greenware in extremely thin layers, and that doesn't seem
>appropriate for most layered slip effects. If you specifically want a
>layered slip effect, where you cut, carve, scrape, or sand through the
>layers to expose successive colors, why would you even be using terra sigs?
>Why not standard slips applied to the leather-hard greenware?
>
>If you give me a little more information I might be able to help you. I am
>a bit of a fanatic about how terra sigs are made, as you can see from my
>terra sig article at
>http://iweb.tntech.edu/wpitelka/professional/terra_sig.htm
>Best wishes -
>- 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/
>
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Vince Pitelka on tue 4 oct 05
Joan -
I think that the results from this are going to be very exciting, and I look
forward to hearing more about your results. Please do keep me informed. I
think you will achieve the best results by doing your layered slip effects
primarily with colored slips applied at the leather-hard stage, and then do
your polished terra sig over the surface, and finally carve back to achieve
your layered slip effects. You will be dealing with carving dry clay
(outdoors, dust mask), but with terra sigs, porcelain/whiteware-based slips,
and Bmix, it should carve beautifully.
Yes, terra sig is not really appropriate under a glaze, because one must
always remember the aphorism "the glaze feeds off the body." In other
words, the clay-glaze interface is a thermochemically active zone, and the
glaze acts as a solvent on the surface of the claybody, incorporating
materials into the glaze mix. So, a very thin coat of slip simply gets
dissolved by the glaze. The best layered-slip effects I have seen have been
unglazed, as in Joseph Godwin's work. You might consider that in thinking
about firing temperatures. You will probably retain a better shine in your
terra sig at cone 04, but you will get better colors in the unglazed slips
at cone 6. It is fairly difficult to get exciting colored clay or colored
slip effects at lowfire without a glaze to "wet" the surface, whereas at
midrange and highfire temperatures the fluxes become more active and the
color intensifies as vitrification occurs. One cannot really call it
"self-glazing," but to see the difference, you only have to compare unglazed
colored porcelain patterns fired to cone 04 and fired to cone 6 or cone 10.
There is one situation where terra sig works great under a glaze. Like any
liquid medium applied to bone-dry ware or bisque-ware, terra sig will settle
more thickly in the recesses and low spots, and thinner on high spots and
flat spaces. In the firing, the glaze will absorb the terra sig where it is
thinnest, but the color will remain where it is thicker. Many low-fire and
midrange potters use this technique to simply make their glazed surfaces
more interesting - they coat the piece overall with terra sig, bisque fire
it, and then go ahead and glaze it normal. The color of the terra sig will
affect the glaze wherever the terra sig is thicker. This would also be an
excellent experiment for any potter firing to cone 6 oxidation who is
seeking more surface variation. Keep in mind that glaze absorption will be
different over a terra sig-coated surface, so a modification of
glaze-application technique might be necessary.
Good luck -
- Vince
Joan wrote:
> I have had success in layering(layers of different colours of terra
> sigillata) on the 2x4 inch test tiles but when I went to 3D forms I had
> cracking and flaking. I may just be applying it in thicker coats on the 3D
> forms. But I am beginning to think that if I want the colours to come
> through I might be better to use slips under the terra sigillata.
>
> I have never done anything like this before....so it is very experimental
> for me. But the idea was to produce sculptures with repeat patterns
> created
> by cutting throught the layers with the top surface being terra sigillata.
> I was using the terra sigillata because I really had no plans on glazing
> any
> of these pieces or if I did apply glaze it would be to make a glaze
> pattern
> on top of the other patterns. I only have access to an electric kiln so I
> couldn't produce the nice look of pit fired or smoked pots.
> Ah yes when I tried glazing some of my test tiles what happened was the
> colours in the red art clay, and the midnight brown/black just got washed
> out. Seems a shame to make terra sigillata and then glaze over it.
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/
Chris Campbell on wed 5 oct 05
Joan -
I think what you are trying to accomplish will
be very exciting to see.
In my work with multiple slip layers, I learned
the most crucial element in each step of the
process was finding the exact right moisture
level needed to work on the pot.
... too soon things went mushy ... to late it cracked.
Also, the slower the piece dried ... the more even
the total surface was ... which made each carving
feel and look the same.
I learned slow drying could mean days
not just hours.
Best of all, I found Bison carving tools ... razor sharp
tools make a world of difference.
Good luck and share images when you can.
Chris Campbell - in North Carolina - revved 'up' for some
rain today ... we are fed 'up' with this drought ! I am going 'up'
to my studio to work on my clay which has been setting 'up'
since last night.
Chris Campbell Pottery LLC
9417 Koupela Drive
Raleigh NC 27615-2233
Fine Colored Porcelain since 1989
1-800-652-1008
Fax : 919-676-2062
website: www.ccpottery.com
wholesale : www.wholesalecrafts.com
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