Kandor,

The relationship between cones and temperature is very vague at best. The
cone is made of ceramic material, and reacts according to the same factors
which mature your work - temperature, time, environment, etc. The pyrometer
only measures ONE of those factors - temperature. You are quite correct in
using the pyrometer as a guide to temp rise only, and the cones as proof of
maturity.

It doesn't matter how accurate a pyrometer is, it will almost NEVER agree
with a cone. I manufacture a digital pyrometer in Australia, and I often
have complaints from customers about this.

You are also correct that soaking equates with additional firing - I think a
20 minute soak may be a bit excessive - 10 minutes would probably be OK for
a kiln that size to equalise - most people don't even bother with a soak as
it is difficult to handle with your type of control system.

I would suggest that you start soaking when the cone is at 3-4 o'clock, and
shut down when it reaches 6 o'clock. That way you avoid overfiring. The
firing is complete when the cone reaches 6 o'clock as specified by Orton.

You can't really overfire bisqueware by soaking, but glazeware might be
affected. How do the glazes look? That is the best indicator of successful
glaze firings - do the colours look OK?

In reality you can use 1" posts - you should get some of these. Get
plenty - they are excellent to have as you can make any size post from 1" to
11" by stacking. The fact that the ware is not exposed to an element does
not usually cause problems, especially since you are using a downdraft
exhaust fan - this causes a good flow of heat through the kiln. It helps to
have all the half shelves at different levels as well, so there is a good
flow - don't have all the half shelves completely closed off at the same
level, which creates many "mini kilns" within the kiln. I would definitely
keep shelves and ware 1" away from the kiln sitter, as it will affect the
cone.

Most people drill 1/4" holes in the lid of the kiln to allow air flow for
the vent fan - in your kiln maybe 6 - 8 holes would be enough. Just space
them evenly around the diameter of the lid - and leave all peep holes
closed. If the lid has a large gap or warps during firing, use some ceramic
fibre sheet to seal the lid.

My website at www.users.bigpond.com/dcoggins has some information on kilns
and firing which may be of interest to you.

Hope this answers all your questions

Dave

"Zander" wrote in message
...
Hi all,

When I was first setting up this kiln I got a lot of great advice from
this
group. I've been set up for a few months now and have completed 2 firing
cycles (bisque/glaze) however, I still qualify as a complete newbie!

The kiln is an electric cylindrical kiln, 7 cu. ft. I have some firing
schedules for bisque and glaze that were passed on to me. I try to
follow
them as best as possible as my kiln (3 zones) has the old lo-med-hi
switches
which don't offer a lot of control. I installed a pyrometer which I rely
on
heavily to monitor rates of change. I also use the kiln sitter and
witness
cones.

My confusion stems mainly from the relationship between the cones/kiln
sitter/ and pyrometer. For example, when bisque firing to cone 04, the
chart states 1940 F at a certain rate for the regular cone. My kiln
sitter is shutting off at 1979 - 1984 which jibes with my witness cones
pretty well. At the point my kiln sitter goes off I check the pyrometer,
and adjust the controls to hold that temperature for 20 minutes. Is this
a good idea? Should I also be holding the temperature when glaze firing
for 20 min? Doesn't holding a temperature just equate to over firing?

More questions: I was told to shut down or start holding when a cone is
at 3 o'clock, the orton book says 6 o'clock.

I have a lot of ware that would fit with 4inch posts but they don't seem
tall enough in terms of having enough elements showing between the
shelves. Do you guys use 4" posts ever?

The height of the kiln sitter tube and my thermocouple tube constantly
conspire to interfere with my post height / shelf placement etc. On my
first shelf I cannot use 6" posts because the shelf will be at the exact
height of the kiln sitter, so I have to use 8" posts which wastes a lot
of vertical room. 4" posts on the bottom level gave witness cones that
were only at 2 o'clock when the center shelf ones were at 6 o'clock. Can
I just ignore the warning about having a shelf within 1" of the kiln
sitter?

I built my ventilation system myself and have never been sure my downdraft
vent is pulling the right amount of air out of the kiln. It's a 4" duct
cap with a 1.25" sq. hole cut into the face of the duct cap. The duct cap
is then screwed to the kiln side with a 1/4" standoff distance, centered
over a 3/8" dia. hole drilled through into the kiln. If I hold a match to
the sighte hole on the opposite side of the kiln with the lid closed it
pulls the flame in for sure, until the kiln gets hot. My lid is also
warped a bit, wouldn't this allow enough air to enter the kiln so I could
keep the sight hole closed up? (at the moment I use the site hole as the
air intake for the downdraft vent.)

If you read this far, Thanks!

Kandor