watering dry clay

Marianne

PS - mentioned the cone discussion to my teacher, and used the words "you
must do such-and-such" (translating to German is not my forte), and she
just looked at me and said "anyone who uses the word _must_ in connection
with pottery....." and the look said the rest! LOL! Think she has a point?

Yes she does. Nice to be reminded of it. As I said, I used to fire gas by
color alone. However the point that most of us were trying to make is that
if you are having problems with your firing, having cones to check your heat
work, certainly makes the problem solving much easier especially when the
conversation is started out with -

"I do think my oven's thermometer might show a bit higher than it actually
is, so maybe just increasing to 1060 or 1070 would help."

Cones are only a tool. They do not make the pudding - they make replication
and problem solving easier (not to mention safety). While I agree with Bob
that with a good controller you don't need cones, I still say that they make
problem solving much easier and that was what this whole thread started out
as. Donna

I love the German look by the by. I don't know why my grandmother didn't
have it. Donna

On Fri, 19 Oct 2007 11:49:21 -0700, "Andrew Werby"
wrote:


"Wes" wrote in message
...
Pardon my ignorance but I bought some fire clay and it is in dry powdered
form. Do I just add water and start stirring? Any idea of weight of
water
to weight of clay? My application is to seal a metal box that will be
used
for case hardening in order to keep air out.

Thanks in advance,

Wes

[Ir doesn't sound like this will work too well, Wes. Clay shrinks
considerably as it dries, while the metal will expand as it gets hot. The
clay won't adhere, and will break up and flake off, making a mess. Can't you
make your metal box seal itself, with bolts? A refractory gasket of some
sort would help; look for ceramic fiber in rope form, or a piece of
refractory sheet material. Here's a link to some of that:
http://www.armilcfs.com/pages/products.htm .]

Andrew Werby
www.unitedartworks.com


Good points! But how about if he used a *clay* box?
To the OP: In the pottery world a "saggar" is a box
made of clay slabs to hold pieces that you don't want
to be exposed directly to kiln flames, or to contain a
special environment around the pieces, They are
typically sealed with some sort of soft clay for the
firing, just as you wish to do.

You can make your own clay slabs by rolling them out with a
rolling pin on a canvas-covered board. Lay down two strips
of wood on ether side to hold the rolling pin up by the desired
thickness of the clay. Probably 1/2 inch slabs would be good,
depending on the size of the box.

The slickest way to do this is to make a template out of tarpaper
(roofing felt). Moisten the back of each template piece and
roll it onto the surface of the slab... it will stick. Now cut out
the clay by running a tool around the template edges... a "pin"
tool (like a smooth-tipped needle on a handle) is ideal for this,
but even an old smooth-edged dinner knife will work,

To assemble the slabs, use an old toothbrush dipped in water
to scuff up the joining faces so they are rough and sticky,
then press the pieces together. Leave the tarpaper on to
give stiffness during this assembly. (Which means you want
to design your template so the tarpaper ends up on the outside.)
The scrubbed clay slurry should ooze from the seams a little.
Smooth it out, and maybe smear a nice fillet on the inside using
additional soft clay.

Let this set up a bit, then carefully peel off the tarpaper.
Drape plastic loosely over it to prevent it drying too fast,
and rearrange the plastic every day or so. When it seems to
be pretty hard all over, remove the plastic and let it
get absolutely bone dry.

You will should fire this saggar once before you actually
use it for case hardening. Set the lid in place when you
do this, to help keep it from warping differently than the
rest of the box. Fire to at least cone 04 (roughly 1050C),
though cone 6 (1200C) might be better.

While I've made plenty of clay boxes, I've never actually
used one as a saggar (not much need for most electric
potters). So one thing I'm not sure of is what sort of clay
mix to seal them with. I *suspect* that if the box has already
been fired, you can use the same clay to seal it with.
I don't think you should let this dry first, just smear it on and
start the firing. However, someone with saggar experience
may have better advice... you might want to mix in some sand
or some other refractory filler with the clay, for example.

Best regards,



Bob Masta

DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Signal Generator
Science with your sound card!

In article , Bob Masta
says...

Good points! But how about if he used a *clay* box?

Would that be sufficiently impermeable to oxygen?

On Sat, 20 Oct 2007 13:22:04 +0100, Rob Morley
wrote:

In article , Bob Masta
says...

Good points! But how about if he used a *clay* box?

Would that be sufficiently impermeable to oxygen?


I *think* so, as long as the box was adequately vitrified
beforehand. But as I have no metallurgical experience
since college (back when dinosaurs ruled the Earth),
I can't say for sure. However, I have heard of this basic
technique being used to maintain a reducing atmosphere
around pottery in an electric kiln (by including combustibles
in the saggar), so it seems at least feasible.

Best regards,



Bob Masta

DAQARTA v3.50
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Signal Generator
Science with your sound card!