Julie Milazzo on wed 8 may 02
Here's what I'm sure is a simple question, with a
simple answer, but I can't seem to get very far. I
have only fired natural gas kilns in the past, and
always went to 4.5 inches for the last several hours.
Now that I have a propane kiln, I asked my propane guy
about the conversion between gas and propane, and he
said to just double the numbers for propane. So, I
began my firing yesterday with the idea that I would
try to climb to nine inches of water column pressure
for this firing. I made it to six, and decided that
even if it took a long time to reach temperature, it
just didn't feel right to go any higher. Using my
dodgy pyrometer, I figured out that I went from one
thousand degees F, to over two thousand within an hour
and a half, and then cones six through eleven all
dropped within the next hour! Thank goodness I didn't
take it to nine inches, but I really would like to
figure out what the propane equivalent to gas is.
Maybe he meant cut in half what I used for gas? But
two inches seems awfully low. Anyway, the extreme
speed didn't seem to adversely affect the clay, though
some of the glazes bubbled a bit (I probably took it
to cone twelve...), and some porcelain pieces slumped
pretty badly. And there is glaze everywhere. However,
they are all recognizeable enough to know that I
didn't screw any of the recipes too badly. The copper
red didn't reduce at all, but the frit recipe from
June seemed to work well. Did pieces not reduce
because of the short period of time they would have
had? I had green flames coming out the spy holes, and
the top, but it was only in reduction for an hour and
a half. Hmmm... Fortunately, the two really good
pieces made it beautifully; I just lost a bunch of
teabowls, which I really have no business making,
anyway. Ahhhh... the wonders of clay... Jules
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Dannon Rhudy on wed 8 may 02
Julie said:
......figured out that I went from one
>thousand degees F, to over two thousand within an hour
>and a half,..... copper red didn't reduce at all.......
For consistent copper reds you need to: start initial
reduction at cone 010 (about 1650=BAF). Best if you can
keep it in slight reduction all the way up, but not=20
necessary. Begin reduction again about cone 9, keep
it there until you shut down the kiln. Copper reds need
TIME during the COOLING cycle. Slow down the cooling
between about 1700=BAF and 1400=BAF, give the reds time to
develop. You might need to relight your kiln, hold it
in that range two-three hours, if your kiln cools rapidly.
Read Pete Pinnell's articles on copper reds in Clay Times
magazine. Don't recall the issues, but you can look it
up on the Clay Times web site.
regards
Dannon Rhudy
Tommy Humphries on wed 8 may 02
Here is that simple answer you were looking for...every kiln is going to be
different, regardless of weather it is propane or methane. The easiest way
to calibrate your kiln is to use a pyrometer to gauge the heat rise at each
raise of pressure. If the heat goes up too fast, cut back on the pressure.
You can chase a kiln like this all night long if you want, or you can chart
a firing then change the settings on the next firing.
I admit it...I am a fiddler, I like to go and fool with the kiln turn this
up, this down twiddle that till it sounds right...others can turn up a kiln
and let it go, till the charts say it is time to turn it up again...only
watching the cones for the final drop.
How much heat you get from 1" of water column depends on your burners, and
your orifices, and the kiln, and the atmospheric pressure and if the kiln
god is happy in there...yadda...yadda...yadda...
Good luck!!!
Tommy
----- Original Message -----
From: "Julie Milazzo"
> Here's what I'm sure is a simple question, with a
> simple answer, but I can't seem to get very far. I
> have only fired natural gas kilns in the past, and
> always went to 4.5 inches for the last several hours.
> Now that I have a propane kiln, I asked my propane guy
> about the conversion between gas and propane, and he
> said to just double the numbers for propane.
Earl Brunner on wed 8 may 02
I can get my Geil to over 1500 degrees F. without registering on the
pressure gauge
and still do a cone 11 firing in 6 hours. I would make a log of every
firing, just
nudge the gas up enough to be able to record the difference on the gauge.
It's not
so much how many inches of pressure you are using as how fast you are
climbing with
what pressure you do use. Your old pyrometer should be fine for that.
My Geil has a digital pyrometer, and you can tell almost instantly how each
small
change is going to affect the rate of temperature change. You might want to
consider that, they aren't terribly expensive.
Julie Milazzo wrote:
> Here's what I'm sure is a simple question, with a
> simple answer, but I can't seem to get very far. I
> have only fired natural gas kilns in the past, and
> always went to 4.5 inches for the last several hours.
> Now that I have a propane kiln, I asked my propane guy
> about the conversion between gas and propane, and he
> said to just double the numbers for propane. So, I
> began my firing yesterday with the idea that I would
> try to climb to nine inches of water column pressure
> for this firing. I made it to six, and decided that
> even if it took a long time to reach temperature, it
> just didn't feel right to go any higher. Using my
> dodgy pyrometer, I figured out that I went from one
> thousand degees F, to over two thousand within an hour
> and a half, and then cones six through eleven all
> dropped within the next hour! --
Earl Brunner
http://coyote.accessnv.com/bruec
mailto:bruec@anv.net
Jon Pacini on thu 9 may 02
Greetings All-----
Julie wrote-----I asked my propane guy
about the conversion between gas and propane, and he
said to just double the numbers for propane.
----The BTU output for 1cu.ft of Nateral gas is 1100 BTU . For Propane it is
2550 BTU per cu.ft. So that is alittle more than doouble. Your propane guy
should have told you to cut your pressure in half, not double it.
Jon Pacini
Clay Manager
Laguna Clay Co
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