When I next fire up the kiln I will check for "ping". The first pots I made
did sound a bit clunky when I tapped on them but I didn't know how they
should have sounded. As my wife kindly gave them away to her sister I can't
now check them. No doubt I will hear if they fall to pieces.

Thank you again for your advice.

Peter
"D Kat" wrote in message
...
When you said you had fired for 17 hours but the the kiln sitter had not
dropped, I was concerned that it was a problem with the sitter - had you
fired that long and at high you should have gone past cone 6 even if you
had done a slow ramp up. Since you did not mention a pool of glaze on
your shelf where the pot had been, I assumed that you didn't over fire to
that extreme of a degree. If you tap on the pot and it pings like glass
then the clay has vitrified - that is it has heated to the point that you
have formed glass within the clay body. That would tell you that you did
indeed reach the temperature that the clay body you are working with
matures to. The closer to greenware the more clunky the sound - the
closer to maturity the more ping. At 03 the clay will still be porous but
less so than 06 or 05 (what I bisque to). You should not be able to
scratch the pot with your nail and it should have changed color if it has
any iron in it (iron bearing clay will go from brown to peachy pink - to
light pink to tan white (tan white is overfired for bisque). White will
go from grey to white with the bisque looking much like the finished
glazeware. It should not feel like glass. If you stick your tongue to
it, it should absorb the water from your tongue rather rapidly but less so
than bone dry greenware. The higher fire the less absorbant it will be.

I was trying to learn if you had overfired or underfired. It sounds
however as if you have things more under control than you think. Marianne
should drop in sometime. She is closer to your neck of the woods and
might know more about your kiln. Let us know how things go.

Donna



9"Peter Holt" wrote in message
...
Hi Donna

Thank you for your reply. I now realise that when I referred to cones of
.3 and .5 I should have said 03 and 05 as you guessed.

Today I visited the shop that sells pottery supplies and found that they
had a spare control switch in stock. I bought it to save a possible
second journey and having fitted it the kiln is now heating up at the
lower settings whereas it wasn't before. I hope that I have solved the
problem but if not I will post again.

You asked if the clay had vitrified but at the risk of displaying the
extent of my ignorance I have to admit that I don't know. The outside of
the bisque looked porous (and absorbed glaze hand painted on to it) but
was relatively hard. Should it have looked and felt like glass?

Thank you for your help.

Peter

"D Kat" wrote in message
...
Let's get the most obvious one out of the way - are you using the small
size cone? This is the size that is used for a cone sitter for our
kilns (US). The larger ones will not bend when needed. It is unlikely
you are making this mistake but one has to ask. You should also be
using the large cones on your shelf to double check what temperature the
kiln is reaching in different locations. You can either get wires to
hold these up, get self supporting ones (more expensive) or simply mold
a clay base. Easy to do - ask if you don't know how. I know Marianne
has said that cones are not used in Europe to monitor heat work but from
what I can see of your kiln, since it appears entirely manual other that
the shutoff switch. You really have to know what temperature your kiln
is firing to and eliminate that as an issue. I don't know what a .3
cone is. I only know of cones going from 022 to 12. 022 being the
lowest temperature (heat work actually) and 12 being the highest. What
temperature are you trying to fire to? If your .3 is our 03 then you
should have certainly reached 1086C in 17 hours - What did your items
sound like when they came out? Had the clay vitrified? What color was
it? Knowing more from you would help. Donna

"Peter Holt" wrote in message
...
I have been given a Cromartie hobby 20 kiln and i have a problem that I
think is with the control switch. Can anyone help?
When I have fired the kiln with a 0.3 Orton cone the cone has not
distorted enough to turn the kiln off, even after 27 hours. When using
the 0.5 cone it has switched itself off on the two occasions that I
have tried it.
I have taken the control switch out and can see that it has an
adjustment knob on it. Can anyone suggest how this works ie which way
should it be turned and how far. It may just be a case of trial and
error but any advice would be appreciated. I am reluctant to buy a new
switch as I am not entirely sure that it is the switch that is the
problem.
You may have gathered that I am completely new to pottery and this is
very much a trial and error project for me. Thanks for any help that
can be offered.