I met someone once that claimed she had a high-fire glue that could be
used to repair ceramics before they went through a cone 9/10 firing.
The glue supposedly survived the high-fire process and thus kept the
piece intact until the glaze hardened. I would appreciate any
information in finding such a glue . . .

Thanks in Advance,

Eric

it was probably a high fire glaze being used as a "glue" - curing at the final
temp. i use basic glaze to fix broken kiln posts - provided the basic kilnpost
support is still in solid compression.

Hi,
I have successfully used mufflers cement for that purpose. Non asbestos variety. Main ingredient is sodium silicate.
Compared to home made sodium silicate "glue" it is economical, it is in a tube- no mess, no drying out...and believe me,
I carry a tube in my handbag at all times (as I sometimes load the kiln im my kids school it is invaluable for quick fix
of broken tails and wings...)
To give a credit to the right person - I was told about it by Margaret Parke.

Happy potting
Andrea

What I would like to know is can I use stoneware body in mid fire range?
what problems should I expect if I do that?
obviously glazes would have to be adjusted or changed.
What do people here think about pros and contras for mid firing comparing to high firing.
I tend to like combination of thrown and handbuilt elements, but lots of them distort or crack in high fire.
Do you think that lowering the firing temp would help??

Thanks for any response
Andrea

A high fire clay would not be vitrified at mid-range. Some, but not all,
glazes would crackle. If you have some clay to use up, go ahead but in
the future, it might be better to get mid-range clays. I've used more
than one high at medium temperatures. One crackled with some glazes,
the other seemed fine. Mid-range clays will never be as dense as
high-fire but some are designed to vitrify. ( That is, unlike low-fire
clay they will not be totally porous )

Glazes are a differant matter. They may not be easy to adjust. I
saw one formula where you substituted Gerstly borate for Neph. Sye.
to lower the firing temp. In an already made glaze, you'd have to
add some mid-range flux to get it to melt. Better to start with
mid-range glazes, unless you really enjoy glaze testing.

Advantages

- wider color range
- shorter firing time
- wastes less energy
- less shrinkage so possibly less liklihood of cracking or slumping

Disadvantages

- less dense clay not as sexy
- harder to get depth in glaze

Elaine

Andrea,

I'd have to agree with all of the advantages that Elaine listed, but I don't
agree with the disadvantages. If you find the right mid-fire clay, it will
be dense and "sexy" and the truth is, you get better color in oxidation at
cone 5/6 versus cone 10. Find some cone 5/6 glazes that look similar to
your cone 10 glazes (if you're happy with the glazes you're using), throw in
some titanium dioxide and you'll get great depth and color variation,
especially if you find a nice combination of glazes for layering. There's
only a 167 degree difference between cone 6 and cone 10, but it takes a lot
longer for that #10 cone to fall and you can't believe the money you save on
electricity. If you're firing in reduction, stick to cone 10. There's
nothing like the glazes you get at cone 10 reduction. You may need a cone
10 clay with more grog if you're experiencing a lot of warping and cracking
in your thrown/handbuilt forms.

I use Standard's #266 which is a very dark brown, dense clay. You really
can't tell whether it's a cone 5/6 or a cone 10 stoneware. The absorption
at cone 6 is 1.4%. A few of their best selling stonewares are 2.0 and 1.5
at cone 10. In fact, they make a red earthenware body, #417, that has an
absorption of 1.0% at cone 02 which isn't too shabby for an earthenware
body. Their cone 6 grolleg porcelain body is .60 absorption and their cone
10 grolleg is .65. Go figure. If a clay is correctly formulated for mid
fire and only mid fire, it will have the same qualities as a high fire clay.
Potters get themselves into trouble when they try to have an "all purpose"
clay body. They want to use it for high fire, mid fire and even raku. It
just doesn't work that way. I know, I've tried and I have a giant "pot
graveyard" to prove it.

Anyway, you can get some beautiful results with mid fire clays and glazes in
oxidation. It just takes a lot of testing to find the right clay and the
right glazes. The Clayart archives is a good place to start. It's full of
cone 6 glaze formulas. Search for "Cone 6 Chit Chat" and you'll find a ton
of them.

Carla

Your ultimate goal is vitrification if you're
going for utility. Otherwise you can fire
at any temp that suits the glaze as a decorative coating only to be
observed.
You can fire a ^10, designed for reduction,
at ^4, oxidation to achieve color response,
but you wont have a very durable piece.

I see no problem with firing a clay made to be used at cone 10 at cone
5. But the fired ceramic may not be fully vitrified when cone 5 drops.
This can leave the clay porous to a degree which would cause problems
in use. Water could enter the clay and cauze severe crazing. To
overcome this the temperature would need to be held for a long time to
ensure complete vitrification. So there may be no savings. The
advantage may be access to a new glaze palette.

Ivor Lewis.

Yes, I wasn't sure what word to use. As whoever replied answered,
a good part of it is using a clay that vitrifies at your range.

I made the observation about the "sexiness" of high-fired clay when
comparing some small human figures I had done in cone ten and in
cone six. The cone 10/highfire was much denser, heavier in the hand,
smoother, all around had more impact. Now this was the university's
all-purpose low to high clay, no surprise it wouldn't be great at
mid-range. Nonetheless of the cone six clays I've tried, I've yet
to find one that had that density, that weight in the hand. Maybe
I will find it.

Elaine