Brian Haviland on thu 8 apr 04
>Hello Clay buds
I finally got the chance (Indiana weather as it goes) to do my first
experiments with
horse hair raku last weekend. I was going to invite a few people when i did
this
but a last min. cancelation on my busy weekend made it possible to jump out
and
get it done ( sorry to sue beach) I will be doing it again real soon... I
put up some pics
@ shutterfly so feel free to take a look at them and please let me know
what you think.
I lost 3 pots to cracks as i was applying hair and 3 out of 7 seems pretty
high to me.
I never lost that many doing reduction cans but i was told that the cooling
rate is much
slower, so thermal shock is not as bad as it is letting them cool in the
open. As this process
uses no glazes (in my case at least) you can't watch the glaze to see
temp.of work so i used
self supporting cones to watch work temp. They work very well for this (See
pics).
I want to say thanks to the list for advice and help received in finding
info. and materials used in
do this firing. The best resource on the world wide web for potters..Amen..
Brian Here is the
link http://www.shutterfly.com/view/pictures.jsp?aid=67b0de21b3fe88396538
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Susan Giddings on fri 9 apr 04
Brian,
I did my first horehair almost a year ago. I learned at a Raku workshop I
took at the Appalachian Center for Crafts last summer.
I do find that breakage due to cracks is high. I try to pull these out of
the kiln at about 1400 F rather than full ^06 that most raku glazes prefer.
I use self supporting cones as well. With no glaze there really isn't much
of a clue as to where you are in temperature except by color and even though
I'm pretty good with that, I don't trust myself! The first pieces I made
with ^10 B Mix. Only 2 out of 6 made it. Next batch, I wedged some grog into
the clay and found that the breakage rate went down significantly - 4 or 5
out of 6 made it. Now, I'm back to using Sheffield stoneware with high
grolleg content. Those with added grog make it. About 1/4 without grog do.
(This is a very smooth, dense and porcelainous body.) I think the grog
helps. I'd like to say that all pieces are thrown the same, but in truth,
those that have cracked have noticeable variation in thickness of walls
evident at the cracks. (Now, who threw those? ;-) ) Also, I find that if I
fire hotter, to 1850 F, regardless of clay body, the rate of cracks/breakage
goes way up.
The piece I did for the stay at home mug exchange is a small horsehair vase.
Page 10 of the mug exchange. I use terra sig a lot on these, I very much
like the color. Also, Ferric Chloride sprayed or painted on gives a good
color. In this case RedArt Terra sig a la Vince's recipe:
http://www.lightonecandle.com/mugexframe.html
I think that breakage is due to thermal shock that is more dramatic just due
to the process as opposed to putting in the reduction cans.
Good luck with it Brian! It is so much fun to do, don't you think?
>
>I finally got the chance (Indiana weather as it goes) to do my first
>experiments with
>horse hair raku last weekend. <<< snip>>>
>I lost 3 pots to cracks as i was applying hair and 3 out of 7 seems pretty
>high to me.
>I never lost that many doing reduction cans but i was told that the cooling
>rate is much
>slower, so thermal shock is not as bad as it is letting them cool in the
>open. As this process
>uses no glazes (in my case at least) you can't watch the glaze to see
>temp.of work so i used
>self supporting cones to watch work temp. They work very well for this
------------------
Susan Giddings
"There are painters who transform the sun into a yellow spot, but there are
others who, thanks to their art and intelligence, transform a yellow spot
into the sun." — Pablo Picasso
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Bruce Girrell on fri 9 apr 04
Nice little kiln there. I'm sure that you found the banding wheel with IFB
to be handy. You did quite well, especially considering that you were
working alone. Lynne and I work as a team with me person handling the
kiln/pots and Lynne concentrating on decorating. I also help manage the
banding wheel. Next time when you have others to help you, I suggest that
you consider the team approach. There is so precious little time during
which the magic works.
> I lost 3 pots to cracks as i was applying hair and 3 out of 7 seems pretty
> high to me.
No. For your first attempts, I would not consider a loss rate of 50% to be
unusual.
> I never lost that many doing reduction cans but i was told that
> the cooling rate is much slower, so thermal shock is not as bad
> as it is letting them cool in the open.
Yes. Also note that the temperature at which you pull the pots is above the
quartz inversion temperature so your pots get to undergo the quartz
inversion in open air.
I have tried various additives - wollastonite, pyrophyllite, talc, and
others to improve thermal shock characteristics and have worked on
developing a low silica clay body to minimize cracking. What I have found
most effective, though, is to throw a thin, uniform pot wall. The thinness
minimizes temperature differences between the outer and inner surfaces and
the uniformity minimizes local temperature differences. In a firing of 30
pots it would be unusual for us to lose more than one or two pots these
days.
The downside of thin pot walls is that it reduces the amount of time
available for decoration. Generally, we have to complete our decoration in
about one minute. After that, the pot is too cold for the horsehair to
stick, though the ferric chloride can still be applied effectively.
> i used self supporting cones to watch work temp.
Just out of curiosity, what cone are you using? We've always used a
pyrometer for horsehair decoration.
Keep up the good work and don't despair those cracked pots. Over time you
will lose fewer and fewer.
Bruce and Lynne Girrell
in northern Michigan, back on the list again after a visit to the southwest,
including a quick stop off to the Clayart room in Indianapolis just in time
for the mug exchange.
Lisa Skeen on fri 9 apr 04
Brian, if you're using a smooth claybody like Bmix or similar to get the grogless, burnished effect, you lose
the thermal shock resistance you get with Raku clay. The only thing I've found to counteract the problem is to
do the firing indoors. I did this once down at Charlie Riggs' studio and had zero loss. Every time I've tried
it outdoors, mega loss. :( LMK if you need some feathers for your pots; our guineas give off zillions.
L
L. P. Skeen http://www.living-tree.net
Living Tree Pottery
Summerfield, NC
> -------- Original Message --------
> Subject: First try at horse hair raku W/pics
> From: "Brian Haviland"
> Date: Thu, April 08, 2004 11:09 am
> To: CLAYART@LSV.CERAMICS.ORG
>
> >Hello Clay buds
>
> I lost 3 pots to cracks as i was applying hair and 3 out of 7 seems
> pretty high to me.
> I never lost that many doing reduction cans but i was told that the
> cooling rate is much slower, so thermal shock is not as bad
Gary Elfring on mon 12 apr 04
BH> I lost 3 pots to cracks as i was applying hair and 3 out of 7 seems pretty
BH> high to me.
BH> I never lost that many doing reduction cans but i was told that the cooling
BH> rate is much
BH> slower, so thermal shock is not as bad as it is letting them cool in the
BH> open. As this process
BH> uses no glazes (in my case at least) you can't watch the glaze to see
BH> temp.of work so i used
BH> self supporting cones to watch work temp. They work very well for this (See
BH> pics).
I fire my horsehair pots to 1800 F, since each one typically has a
liner glaze inside it. (Functional horsehair! )
Only one in 9 or 10 cracks. To avoid cracks you need to make sure you
use a clay specifically designed for raku. I use the smooth
"porcelain" raku from Great Lakes Clay. It is as smooth as porcelain,
no grog, and rarely cracks. You also need to make sure your pot walls are
very even.
When I fire, I typically have 1 horsehair pot in the kiln along with 1
or 2 other normal raku pots, that go into reduction cans. I pull the
reduction pieces first, so that the horsehair pot cools a bit before
leaving the kiln. Then the horsehair piece goes onto a soft brick that
sits on a banding wheel. Here are some samples:
http://www.elfringpottery.com/horsehair.htm
--
Best regards,
Gary
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