Susan Setley on thu 5 feb 04
=?ISO-8859-1?Q?Raku=3F?=
In a message dated 2/5/04 8:43:19 AM, wschran@EROLS.COM writes:
>
> Yes, you're correct, cones measure "heat work", but they are only
> accurate if the temperature rise is a specific amount of rise over a
> specific amount of time. The cones will bend at a higher or lower
> temperature if the temperature rises faster or slower than the
> specifications written by the manufacturer. In this instance, when a
> firing takes less than an hour, I would think a pyrometer might
> provide a better device for judging temperature.
>
We have an older, somewhat leaky kiln. The fastest it has ever been fired has
been about 90 minutes, and typically it takes 2 hours.
Pyrometers can go terribly wrong, esp. in the hands of amateurs (that would
be me -- grin). I spent an entire weekend following an experienced Raku artist
around like a puppy dog watching everything she did. She showed me how to set
the studio's pyrometer, which is run by a computer chip and can measure any of
several kilns. Most of the pyrometers are hard-wired but there is one on an
extension for the outside kilns.
So then my friend and I do our first firing. No matter what we do, we can't
get the temp to rise. Our pieces had been in for over four hours and the kiln
was barely moving. Finally at 11PM we took them out even though the pyrometer
said it wasn't anywhere near done. We just couldn't stay any longer.
Meanwhile another potter was hovering nearby. She had tried to help us get
the kiln firing faster. I had taken the pyrometer out and it was in an external
hole in an electric kiln to protect it while it cooled. The other potter
noticed something odd -- the temp reading wasn't going down even though the probe
had to be cooling.
She looked -- someone had come through the kiln room, RESET the readout to
read a DIFFERENT kiln -- and left for the day. We were so inexperienced that we
didn't know the readout could be for any of four kilns in the kiln room as
well as for the probe. OOOPS!
MAN were those pots overcooked!
Nothing's perfect, but we tend to take pots up a little more slowly to about
500 degrees; then crank it up to 1,000, and then let it RIP until we get to
1750. It seems to work well for that kiln and we have very few broken pots. We
also fire it up to 1,000 more slowly if there are refires in there.
I can't say this is the only way or the best way but it's the combined
experience of about a dozen potters with that kiln in that setting.
And -- just for the record -- I did NOT recommend that beginners open Raku
kilns and pull pots in shorts. I said I know someone who does that. I don't
think it's a big deal to wear long pants for 1/2 an hour -- even on a hot summer
day. Far better than a bad burn.
Susan Setley on thu 5 feb 04
=?ISO-8859-1?Q?Raku=3F=A0=20maybe=20an=20easier=20solution...?=
In a message dated 2/5/04 7:17:50 PM, lleary@EPIX.NET writes:
> Here's my question ....why use a pyrometer or cones at all for raku?
> I've always have great results just by watching the kiln and glazes
> closely.....Of course this works only for glossy glazes.=A0 For dry, matte
> glazes you can either fire a glossy piece at the same time or you can
> learn to approximate what temp the kiln is at by the color inside the
> kiln.=A0=A0 (orange, yellow-orange, yellow, ect.)
>=20
I think looking is a great way to double-check the pyrometer, but if you=20
really want to control how fast the kiln fires, as we do -- in stages -- a=20
pyrometer is the only practical way to do it. We like to fire it more slowly=
to 500=20
degrees, faster to 1000, and then open it up the rest of the way. We also do=
it=20
more gently when we have refires. Even though each class is always half=20
beginners, we very rarely have a piece break.=20
Keep in mind that this is a brick kiln that really needs to be rebuilt. It's=
=20
the only Raku kiln I have experience with. Other kilns may fire more=20
predictably.
" CAUTION: If your
glazes goes 'ugly' for a second time, it's usually overfired and there
is not much you can do with it."
Well you can refire the piece. What do you have to lose? :)
I did that last week with a piece that got seriously overfired. What an=20
improvement. :)
Susan Setley on thu 5 feb 04
=?ISO-8859-1?Q?Raku=3F=A0=20maybe=20an=20easier=20solution...?=
In a message dated 2/5/04 8:56:22 PM, lleary@EPIX.NET writes:
> If you prefer a pyrometer, that's fine. But you would be amazed at just
> how accurate one's judgement of kiln temp by color can be after a bit of
> experience.=A0
>=20
Actually I wouldn't, because we also judge visually. :) The thing=
the=20
pyrometer helps is controlling how fast it fires. I don't think anyone shoul=
d=20
infer from anything I wrote that the pyrometer is the only thing to use. We=20=
do=20
look at the pots and the color of the kiln as well as the state of the=20
glazes. In addition, we use the pyrometer to provide us control *=
before* the=20
kiln gets to that point. Does that make more sense?
"I have to say though, I don't agree with you about the overfiring.=A0 I've
never seen an overfired raku pot that looked like anything other than it
is....an overfired pot."
I've got one I was very unhappy with the first time and very happy with the=20
second time. I probably will not sell it because I want it for myself. It we=
nt=20
from a real dog to a real keeper.
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