LindaBlossom on wed 5 nov 03
Hello Ron,
I'll answer by using the cut and paste method so I don't miss or fail to
answer something:
> I am just putting two and two together - If Stephen Hill - who single
fires
> all his pots to cone 10 - says - treat the first part of a single firing
as
> you would a bisque then he has learned the hard way.
I don't disagree with this. I have always fired at about 100C per hour. My
rate was determined by the thickness of the work. When I fire murals that
are around 3/4" thick and sinks with joinery, I have always kept this rate.
This rate was determined by thickness and moisture, not by the presence of
paper in the clay. When I fire things 2" thick I slow down to half that
rate. What I learned though was that thin work could be fired much faster
whether it was first firing (single fire) or refires. With tiles thinner
than 1/4" I can push the rate to 250C/hr. I haven't tried anything faster.
Again, I am always thinking of moisture, not paper.
>
> What he is saying is - when glazes start to seal over - they prevent the
> burning out of organics in the clay. If there is iron in the clay then the
> iron will reduce and become a flux, cause pinholing and blisters and
> overfire the clay.
> You did not answer the question - is your clay white? If it is then
perhaps
> that is part of the reason you are not having a problem. Besides - if one
> side is not glazed then the organics can come out the unglazed side easier
> than if they were glazed.
I have red clay - there is Neuman Red in my clay. I wonder about the
migration of organics. When the paper that is in clay directly below the
glaze burns out do we expect it to travel the thickness of the piece to get
out more easily? I could make a few tiles with feet and glaze them on both
sides and fire them in my next firing just to see if it makes a difference.
>
> The 2nd part of this - at cone 6 there are many glazes that have a lot of
> boron - these types of glazes seal over at quite a low temperature - and
> can prevent the organics from getting out in ware glazed on both sides.
>
> There may even be some high boron glazes that will not be usable in single
> firing - to any temperature because of this.
I just checked my glazes and found several that contain boron and one in
particular that I use a lot contains it. I also layer glazes, sometimes
five glazes to produce the look I want so there is quite a mix of
ingredients on some of my surfaces. (don't worry - I do the olive oil and
lemon tests on tiles that will be in kitchens)
> If we speculate based on what we know we can anticipate problems so that
> when they show up we may have some idea about the causes - and find
> solutions.
>
> It is about thinking about what we do and accumulating the ways to deal
> with our particular ways of working. Knowing that paper clay has extra
> carbon in it and that it will never be water tight can lead to appropriate
> uses of the material. - knowing the limitations of our materials will
help
> us decide how to use them.
True but these thoughts produce theories and theories must be tested,
wouldn't you agree?
Linda
>
>
>
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Ron Roy on thu 6 nov 03
Hi Linda,
I also meant to ask - do you have a vent running - kiln vents go a long way
to keeping oxygen resupplied - I would advise anyone single firing or even
bisquing ware to consider having one.
I do think it would be of use to us all if you would do some testing - a
glaze with lots of boron on different thicknesses of clay completely glazed
and set on clay feet.
I can tell you which glazes would have the most boron if that will help -
or I can furnish one.
I do agree that testing is appropriate but it is even more appropriate to
have a back ground of understanding so that we can deal with problems that
show up.
It is also appropriate to understand as much as we can so that we can
design the proper tests to prove or disprove theories.
We - as a group - are having to learn about our craft all over again
because the so much has been ignored over the last 50 years. There are new
technologies to deal with as well - like paper clay and microwave ovens. If
we don't make some attempt to think our way through the possible problems
then we will pay the price. This is about understanding more than proving
and disproving.
RR
>I have red clay - there is Neuman Red in my clay. I wonder about the
>migration of organics. When the paper that is in clay directly below the
>glaze burns out do we expect it to travel the thickness of the piece to get
>out more easily? I could make a few tiles with feet and glaze them on both
>sides and fire them in my next firing just to see if it makes a difference.
>
>>
>> The 2nd part of this - at cone 6 there are many glazes that have a lot of
>> boron - these types of glazes seal over at quite a low temperature - and
>> can prevent the organics from getting out in ware glazed on both sides.
>>
>> There may even be some high boron glazes that will not be usable in single
>> firing - to any temperature because of this.
>
>
>I just checked my glazes and found several that contain boron and one in
>particular that I use a lot contains it. I also layer glazes, sometimes
>five glazes to produce the look I want so there is quite a mix of
>ingredients on some of my surfaces. (don't worry - I do the olive oil and
>lemon tests on tiles that will be in kitchens)
>
>
>
>> If we speculate based on what we know we can anticipate problems so that
>> when they show up we may have some idea about the causes - and find
>> solutions.
>>
>> It is about thinking about what we do and accumulating the ways to deal
>> with our particular ways of working. Knowing that paper clay has extra
>> carbon in it and that it will never be water tight can lead to appropriate
>> uses of the material. - knowing the limitations of our materials will
>help
>> us decide how to use them.
>
>True but these thoughts produce theories and theories must be tested,
>wouldn't you agree?
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
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