Estelle Renberger on fri 18 may 07
Bonnie's post concerning getting color in smoke firing has inspired me to try the process one more time. But before I start, I'm hoping someone on this list can give me a clue as to why my pit or smoke fired pots have always turned out completely black. Just black. I bisque fire to 04, wrap the pieces in colored paper, fire in sawdust, plus available combustables such as dry leaves, pine needles etc. I add crumpled newspaper and various organic materials and sprinkle copper carb and iron ox into the mix. But my finished product is always black. Just black. Any suggestions would be appreciated!
Estelle
Vince Pitelka on fri 18 may 07
Estelle wrote:
"Bonnie's post concerning getting color in smoke firing has inspired me to
try the process one more time. But before I start, I'm hoping someone on
this list can give me a clue as to why my pit or smoke fired pots have
always turned out completely black. Just black. I bisque fire to 04, wrap
the pieces in colored paper, fire in sawdust, plus available combustables
such as dry leaves, pine needles etc. I add crumpled newspaper and various
organic materials and sprinkle copper carb and iron ox into the mix. But my
finished product is always black. Just black. Any suggestions would be
appreciated!"
Estelle -
The reason that your pots are turning black is because you are just sawdust
firing, and the temperature is so low that nothing else can happen. Sawdust
"firing" is not really a firing process, because it does not attain a
high-enough temperature to qualify as a firing process. It is a cosmetic
process, and I try to refer to it as "sawdust smoking." All you are doing
is impacting carbon into the clay and/or slips. It can be very beautiful in
the variegated smoke effects, but you cannot expect more than that.
If you want to get other colors, you need to do pit-firing or sagger firing.
In pit firing, the wares are placed in a pit bedded in sawdust, copper
sulfate, steel wool, copper scrubby pads, copper wire, twine soaked in salt,
oil-soaked rags, and/or other materials. A standard bonfire is built above
the pit, and the coals slowly burn down through the sawdust, bringing the
wares to a much-higher temperature than in the sawdust smoking process.
In sagger firing, you place the wares in a reuseable refractory container
(the sagger) and fire it in a conventional gas kiln. You don't want to do
this in an electric kiln, because the fumes that escape from the sagger will
harm the kiln elements. The effects will be determined by the materials you
place in the sagger, and the temperature you fire to.
Good luck -
- 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/
Taylor Hendrix on fri 18 may 07
Estelle,
Sounds to me like you are firing with mostly packable combustibles and
not letting in enough air. What I mean is that all the sawdust, paper,
leaves, and pine needles can leave very little space for air to get in
and oxidize parts of your pots. These things also produce a bunch of
smoke (those needles especially) and that will blacken up most things.
If the ash and unburned material keep the pot from re oxidizing you're
likely to get a black pot. I turned several aluminum foil saggared
pots completely black with just a few strips of salt soaked cardboard
and one or two pine cones. Black as night, but boring to me.
Add pieces of wood and twigs to your burn, don't cover your pots with
too much sawdust, and play with whatever lid (if any) you are putting
over your burn. When you unload, pay attention to how much stuff is
left unburned. That will give you a clue as to how much air you are or
are not getting into your setting.
In my pit I seldom cover my pots completely with sawdust. It's usually
just a cushion for the bottom. Plenty of twigs etc cushion much larger
pieces of wood placed on top. I want it to get HOT so my chemicals
will flash color. I do believe I have some loading pics of my pit you
can look at on flickr. See the bottom link in my sig.
On 5/18/07, Estelle Renberger wrote:
> ...But before I start, I'm hoping someone on this list can give me a clue as to why my pit or smoke fired pots have always turned out completely black. Just black. I bisque fire to 04, wrap the pieces in colored paper, fire in sawdust, plus available combustables such as dry leaves, pine needles etc. I add crumpled newspaper and various organic materials and sprinkle copper carb and iron ox into the mix. But my finished product is always black. Just black. Any suggestions would be appreciated!
>
> Estelle
--
Taylor, in Rockport TX
http://wirerabbit.blogspot.com
http://wirerabbitpots.blogspot.com
http://www.flickr.com/photos/wirerabbit/
Lynne and Bruce Girrell on sat 19 may 07
Vince Pitelka wrote:
>Sawdust "firing" is not really a firing process, because it does not attain
>a high-enough temperature to qualify as a firing process. It is a cosmetic
>process, and I try to refer to it as "sawdust smoking."
An excellent distinction, Vince.
At one point I was trying to get some smoke effects with an aluminum foil
saggar and consistently overfired until a friend talked about the process as
a smoking process, rather than firing. Suddenly the lightbulb fired. I got
the next pot just hot enough to accept the smoke and it came out just like
it was supposed to.
Bruce Girrell
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Bonnie Staffel on sat 19 may 07
Estelle, I think you are doing what is called "sawdust" firing, not pit
firing. Pit firing consists of a roaring bonfire with a lot of wood and =
it
takes at least a day or more to cool down, and not much sawdust except =
at
the bottom of the pit. If your pots are covered with sawdust, then that
material just smolders away, making very smoky black pots. There is not
enough heat to vaporize the copper either. =20
For a simplified pit fire, look at the Blog site on my Website listed =
below
under Trash Can Firing. I explain how to do it without digging a hole =
in
the ground. The same principles are used, but on a larger scale in the
ground.
My colored smoke fire is just that, a quick lighting of a few pieces of
newspaper and it is over in just a few minutes. =20
I hope this explains the different methods so that you can start your =
search
for understanding. =20
Bonnie Staffel
http://webpages.charter.net/bstaffel/
http://vasefinder.com/bstaffelgallery1.html
DVD Throwing with Coils and Slabs
DVD Introduction to Wheel Work
Charter Member Potters Council
sacredclay on sat 19 may 07
One experience in a college saggaer firing in a raku kiln lead me to
believe that it may more likely be the type of clay you are using. I
was using white raku clay and got all of these beautiful pinks and
mauves. The other person was using stoneware, which led hers to be all
gray and black. both fired in the same saggaar at the same time. That
may be one clue. Kathryn in NC
Dannon Rhudy on sun 20 may 07
What temperature do you fire to for your pit firing?
I have always found that for the best color - reds, iron
browns, salt oranges, etc, it is necessary to reach a
temp of 1500F to 1650F. At lower temperatures
the salts do not volatize with any degree of regularity.
There are other reasons for purely black pieces, but
temperature is a definite indicator.
regards
Dannon Rhudy
stephani stephenson on mon 21 may 07
i use to do a lot of pit firing, sawdust firing and
saggar firing, and though i came to favor saggar
firing, i did get decent flashing and coloration in
my sawdust firings...
a very smooth bodied , burnished clay or terra sig
was best.also you can bisque the ware if you do it
very low.
and , as Taylor mentioned, one key is to make sure
there is some oxidation . i use to create 'oxidation
pockets' in the sawdust.
for the firing I used the typical built up brick
enclosure with metal cover..sometimes i would leave
small gaps in the brick, but also i would put random
pockets of broken bisque,etc. in the sawdust.
these would take up space in the enclosure and allow
air in in localized areas.
i would also wrap little packets of copper and/or
yellow iron oxide, mixed with with epsom salt , borax,
salt or bicarb of sodium
etc, and place them next to the piece, or paint or
spray YIO and CuCarb on the piece.. i don't know
which of any of the auxilliary materials was actually
promoting flashing, but i did get some interesting
effects from one or more of them...
even though the sawdust fire is not very hot on the
whole, small localized areas,can get pretty hot, hot
enough to promote flashing...
but, the black indicates deficincy of oxygen, too
much reducing .and carbon.
so try it again!
also i fired some i fired some rather large slab
pieces in sawdust...and successfully...later i was
told "you can't do that, large pieces will break"
so lesson is, sometimes it works even if it isn't
'supposed to'!
Stephani Stephenson
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