Paul Herman on sun 3 nov 02
Hi Woodenheads,
I just have to chime in with Vince on this one. Where I live is one of
those places where there is not much hardwood around, so we burn mostly
conifers. Dead Ponderosa Pine and White Fir (Piss Fir, in the local
vernacular) are easy to get, so that's what we use. Piss Fir gives off
remarkably pungent odors during cutting and burning. However, the limb
wood from these species is definitely hard even though it's a
softwood (!?).
The kiln smokes black right after a stoke, then shortly burns with a
grey transparent smoke for several minutes, then clears and we stoke
again. It smokes more when the temperatures are low, and as they climb
the kiln seems to burn cleaner. During the latter 24 hours of the
firing, when it's really cookin, stokes are 8-10 minutes apart.
We have not had problems with excessive coal-raking or clogging under
the grate. I attribute this to making the grate tight enough. In my
(very limited) experience, I've helped fire a few other woodkilns.
Several of them had grates that were so loose that the fuel fell through
too rapidly, resulting in clogging of the airways with coals, then the
raking and shoveling started. I think if you are shoveling coals, then
your grate is too loose. Our grate has gaps of about 1". During the last
24 hours we poke under there a bit, and this time pulled out about a
half gallon of ash.
We have been burning some hardwood in the side stokes, (eastern oak
scaps from a molding factory), and it makes some very interesting drippy
matt glazes on the pots in that area. Pine and Fir seem to make shinier
glazes. The front face of the setting, right next to the main fire, is
nice and shiny.
I'm still evaluating the last firing, and have to say that I'm really
pleased. All the rest of the crew seems happy. If you have to be insane,
this is a pretty good way to be so, IMHO.
Best wishes,
Paul Herman
Great Basin Pottery
423-725 Scott Road
Doyle, California 96109 US
potter@psln.com
----------
>From: vince pitelka
> There has been some careless language regarding the use of pine versus oak
> in woodfiring. It has been implied that pine automatically produces much
> more smoke, and that is not the case. It depends on kiln efficiency and
> firing practices. Up in the Rockies and other mountainous locations there
> are woodfire potters who cannot get hardwood, and therefore fire with
> spruce, fir, and pine. Elsewhere there are plenty of woodfire potters who
> fire with pine because they prefer the results, as Mel pointed out.
vince pitelka on sun 3 nov 02
There has been some careless language regarding the use of pine versus oak
in woodfiring. It has been implied that pine automatically produces much
more smoke, and that is not the case. It depends on kiln efficiency and
firing practices. Up in the Rockies and other mountainous locations there
are woodfire potters who cannot get hardwood, and therefore fire with
spruce, fir, and pine. Elsewhere there are plenty of woodfire potters who
fire with pine because they prefer the results, as Mel pointed out.
Pine is pitchy, and that pitch produces a fast release of hydrocarbon gases.
If you stoke too much pine at once, of course you are going to get billowing
smoke, much more than when you stoke too much oak. It is simple combustion
chemistry. Flames are just the hydrocarbon gases oxidizing (combusting) as
they leave the surface of the heated wood. Smoke is unoxidized carbon
carried through the kiln and out the stack. In the intense heat of the wood
kiln firebox, pine oxidizes very quickly, releasing huge amounts of carbon
and hydrocarbon gases. Too much stoking, and you get way more carbon and
hydrocarbon gases than can be combusted inside the kiln, so you pollute the
atmosphere.
I think that part of the problem here is the assumption that you need a
major coalbed to effectively fire a wood kiln. That seems to be a popular
woodfiring legend. The size/depth of coal bed is of course a product of the
type of wood and the speed/efficiency of combustion, but if you are getting
efficient combustion for good heat gain, then the size/depth of the coalbed
is less of an issue. In general terms, the intense heat from the coalbed
supercharges combustion, but again, that's a non-issue if you are getting
good heat gain with less of a coalbed. If you are burning pine, as Karen
points out, you have to stoke less each time but you have to stoke more
often to maintain good heat gain. If you have to (or choose to) burn pine,
then you accept that regimen.
Of course, it is mighty fine to stoke a bunch of oak and then sit back for
fifteen or twenty minutes before you have to stoke again.
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
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