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Posted by Peter Holt on December 23, 2007, 4:24 pm
Please log in for more thread options 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
> 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
>
>
>
>> 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" disisdkat@hotmail.com> 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
>>>
>>>>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.
>>>>
>>>
>>>
>>
>>
>
>
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