John Tiemann on wed 28 apr 04
I am reposting the following message in case it was missed. I have not received any feedback yet, and I know there are others out there with the same questions. Thank you.
Hello all,
I have been wanting to do some saggar firings with my high school
students. We usually fire up the Raku kiln with the weather getting nicer,
but I thought of trying to do some saggar firings in the raku kiln
instead. I have a few questions if you would be willing to help me and my
students out...
1. Is it true that saggar firing in an electric kiln is bad for the
elements? I remember seeing an article in either clay times or PMI that
talked of firing saggars in an electric, but others told me it was bad
for the elements even with proper ventilation.
2. What temperature do you try to reach when firing a saggar in the
raku kiln? I have heard mixed results anywhere between ^08 - ^10. Is this
temperature inside the saggar or the kiln?
3. At what temperature does the burnished "shin" fade from the piece?
4. How much cooler is it inside the saggar than outside in the kilns
atmosphere? How do you compensate for this?
4. I have made a ceramic jar for the saggar... do you use a lidded
container or build the saggar out of kiln bricks? What seems to have
better results?
5. Do you seal the lid of the saggar with kiln wash or a kiln shelf?
How much smoke do you want comming out of the saggar (How much is too
much?)
6. How fast/slow do you allow the kiln to cool before removing the
saggar?
7. What materials (combustibles/chemicals) do you find to work best
with your saggar firings? I know many materials are toxic, what do you
recommend staying away from with high school students? (aluminum foil,
copper sulfate, etc.)
I know this is a lot to ask, but any help would be greatly appreciated!
Thanks so much for your time and I hope to hear from you soon.
John Tiemann
St. Louis, Missouri
Terri Kennedy on thu 29 apr 04
Hi John,
I do electric saggar firings for approx. 3-4 years now and so far I haven't
noticed any difference in the life of my elements, at all. I use that kiln
also for other firings (glaze and bisc) and haven't noticed any difference in
those firings either.
I do my saggar a little different from most, but I think I get quite a
variety of colors doing it this way. I bisc to ^06 and then saggar to either ^07 -
06. So actually I'm firing quite high compared to most people who saggar
fire. I'm not sure when the burnished sheen fades from the piece, but I do know
that the pieces that I burnish still have quite a sheen after both firings.
You can make your own saggar from all that you described but I find it easier
to just go to Walmart or home depot and buy a regular terra cotta flower pot
and use that. It seems I get just as many firings out of that pot as then
ones I used to throw. Each holds up approx.2 - 3 firings. Then just put a kiln
shelf as the lid. Never have noticed smoke coming from them, but it does
smell...so keep the place well ventilated.
It seems to do better with a quick firing...fast up to temp and then quick
cool. Some of the ingredients that give good colors and are safe,
are...toothpaste which makes a blueish color...Ketchup ,mc donalds seems to give the best
results and fires redish color... steel wool makes a crackle or horsehair
looking lines...oranges, especially satsuma's if you can find them, make a dark
orange and saw dust makes black or brownish, great to darken inside of vessels.
Some others that give good colors but are questionable in fume safety, salt,
especially sea salt like seaweed, make beautiful peaches.... cobalt carb makes
a real BRIGHT blue... copper wire does fabulous, black lines.... old medicines
make tons of colors, it just depends on which one.
Hope this helps some.
--Terri Kennedy
Denham Springs, LA
Potterri
*"Growing older is mandatory, but growing up is optional!"
Vicki Hardin on thu 29 apr 04
John, you will probably find tons of information on this in the archives,
but I will give this a shot.
> 1. Is it true that saggar firing in an electric kiln is bad for the
> elements? I remember seeing an article in either clay times or PMI that
> talked of firing saggars in an electric, but others told me it was bad
> for the elements even with proper ventilation.
I have not done this as I fire my saggars in a pit which give me an excuse
to burn something. I have heard that it is not a problem in an electric
kiln as long as the temp is not exceeded.
> 2. What temperature do you try to reach when firing a saggar in the
> raku kiln? I have heard mixed results anywhere between ^08 - ^10. Is this
> temperature inside the saggar or the kiln?
I saw Randy Brodnax weekend before last fire an aluminum saggar in a trash
can. Thats not a trash can lined with fiber. I mean a plain old you could
dump your trash in it trash can. He said to fire until the aluminum starts
to burn away at the bottom. The aluminum then makes a tent for the fumes
from ferric chloride, salt and copper sulfate to create incredible color on
the piece. Take care with the chemicals, they are caustic.
> 3. At what temperature does the burnished "shin" fade from the piece?
Don't go above 011 if you want the sheen to remain. Some people burnish and
then high fire, but like that affect.
> 4. How much cooler is it inside the saggar than outside in the kilns
> atmosphere? How do you compensate for this?
Hmmm don't know.
> 4. I have made a ceramic jar for the saggar... do you use a lidded
> container or build the saggar out of kiln bricks? What seems to have
> better results?
I have seen people use saggars that they threw. I understand they don't
last long. But if I were doing it this way, rather than stacking all those
bricks in my electric kiln, I would just throw a tight fitting lid for the
saggar. Kiln shelves and bricks seem a little more appropriate for a gas
fired kiln.
> 5. Do you seal the lid of the saggar with kiln wash or a kiln shelf?
> How much smoke do you want comming out of the saggar (How much is too
> much?)
I would not seal the saggar. The smoke coming out of the saggar will
depend on how much combustible you put in the saggar versus how large your
saggar is and how long you intend to fire. Some people fire to 08 just as
if firing a bisque kiln. Others turn the kiln on and let it climb to
temperature on high shutting off. This I think is harder on my kiln than I
would like.
> 6. How fast/slow do you allow the kiln to cool before removing the
> saggar?
Let cool normally. Take out when cool.
> 7. What materials (combustibles/chemicals) do you find to work best
> with your saggar firings? I know many materials are toxic, what do you
> recommend staying away from with high school students? (aluminum foil,
> copper sulfate, etc.)
Like I said above copper sulfate, (Root Killer from Wal-mart) Ferric
Chloride (echant from Radio Shack) and rock salt. Saw Dust and horse hair
is good too. I would not want to breathe that in an enclosed room. Consider
pit firing outside or using your raku kiln.
Also, Edurado Lazo has an excellent article on pitfiring at
http://www.vickihardin.com/articles/pit-fire-ceramics.html that may give you
some ideas about the use of chemicals.
Good Luck,
Vicki Hardin
http://ClayArtWebGuide.com
Snail Scott on thu 29 apr 04
At 09:37 PM 4/28/04 -0700, you wrote:
>1. Is it true that saggar firing in an electric kiln is bad for the
>elements?
Only if it leaks. An airtight saggar is safe
enough. The leakier it is, the more damaging it
is to the elements. They won't die instantly in
any case; they'll just have a shorter lifespan.
>2. What temperature do you try to reach when firing a saggar in the
>raku kiln? I have heard mixed results anywhere between ^08 - ^10. Is this
>temperature inside the saggar or the kiln?
The the temperature inside the kiln but outside
the saggar is totally irrelevant. If the work is
all inside the saggar, that's where it counts.
If you don't have a way of measuring that, you
will have to do a few trial-and-error firings.
A long soak will tend to let the temperatures
equalize, though.
>3. At what temperature does the burnished "shin" fade from the piece?
About ^010, in my experience. Logically, this
could vary slightly with the clay body, but
as a rule of thumb, I try to keep burnished-
clay firings below ^010 to be safe. It doesn't
dull instantly, though, as if some magic line
had been crossed. The higher the temperature,
the lower the gloss, but some evidence of the
burnishing will remain even at stoneware
temperatures. It won't be shiny, though; just
'different'.
>4. How much cooler is it inside the saggar than outside in the kilns
>atmosphere?
Depends on the speed of the firing. In a fairly
slow firing, there may be almost no discrepancy.
For a fast firing, you'll need to do some
trial-and-error firings to calibrate for your
particular firing speed, saggar density, etc.
>...do you use a lidded
>container or build the saggar out of kiln bricks?
Kiln bricks are easy and more flexible. A jar
would have the convenience of removability and
re-use, and be less leaky. Never used one myself,
but that doesn't mean it's a bad idea.
>5. Do you seal the lid of the saggar with kiln wash or a kiln shelf?
I don't get this question - how are kiln wash
and a shelf interchangeable? (Do you mean using
a purpose-made lid on the jar mentioned above
or using a shelf?) I've only used a shelf, but
as mentioned above, that doesn't mean much.
>How much smoke do you want comming out of the saggar (How much is too
>much?)
Again, it's a progressive thing. Keep it to a
minimum. The more smoke, the more damage. Where
you draw the line isn't a decision I can make.
>6. How fast/slow do you allow the kiln to cool before removing the
>saggar?
Doesn't matter. The only part that matters is
how cool the work inside the saggar is when
that work hits the open air. Since the work
is typically very low-fired, there's very
little thermal-shock potential to worry about,
though.
>7. What materials (combustibles/chemicals) do you find to work best
>with your saggar firings? I know many materials are toxic, what do you
>recommend staying away from with high school students? (aluminum foil,
>copper sulfate, etc.)
No harm in aluminum foil. Copper sulfate and
other copper materials: keep back or ventilate
well, or both. Metallic copper is fine to handle,
though (like brass filings or copper wire and
pot scrubbers); just don't breathe the fumes.
Banana skins and glossy magazine pages can be
good, and salt.
-Snail Scott
Reno, Nevada, USA, Earth
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