Ivor and Olive Lewis on sun 5 aug 07
As Mel says, in the end we have to get down to the Science and =
Technology.
Without going into detail I was taught that reduction should not begin =
until after the clay commenced its maturing cycle but must happen before =
the lowest melting point glaze ingredient started to fuse. The first =
instruction to ensure carbonaceous materials were removed by burning, =
the second so that the reducing medium could diffuse into the glaze and =
complete the reduction chemistry.
I was also taught that once glazes had fully matured it was difficult =
for reducing gases to permeate into the fused surface and do further =
work, thought oxygen at high temperature could affect surface colour. =
This may explain why I have had many pots that should have been copper =
red all round that had a green windward side and a red leeward side.
The final point was that if I wished to change the grey colour of a =
reduced Iron bearing clay this could be achieved by allowing air to =
invade the kiln between 800 and 700 deg C as the kiln cooled.
Those observations that reduced glazes which have been reoxidised on =
cooling are brighter suggests something happening at the molecular =
level.
As one of my Physics Teachers would say, "Go back to First Principles".
Best regards,
Ivor Lewis.
Redhill,
South Australia.
Ron Roy on mon 6 aug 07
Just to add something here I think is important.
If reduction is started too late - after a glaze has sealed over the clay -
the clay will not be evenly reduced. You will see the effect when you break
the ware - different colours of the body. The clay should be evenly reduced
all the way through.
RR
>Without going into detail I was taught that reduction should not begin
>until after the clay commenced its maturing cycle but must happen before
>the lowest melting point glaze ingredient started to fuse. The first
>instruction to ensure carbonaceous materials were removed by burning, the
>second so that the reducing medium could diffuse into the glaze and
>complete the reduction chemistry.
>I was also taught that once glazes had fully matured it was difficult for
>reducing gases to permeate into the fused surface and do further work,
>thought oxygen at high temperature could affect surface colour. This may
>explain why I have had many pots that should have been copper red all
>round that had a green windward side and a red leeward side.
>The final point was that if I wished to change the grey colour of a
>reduced Iron bearing clay this could be achieved by allowing air to invade
>the kiln between 800 and 700 deg C as the kiln cooled.
>Those observations that reduced glazes which have been reoxidised on
>cooling are brighter suggests something happening at the molecular level.
>As one of my Physics Teachers would say, "Go back to First Principles".
>Best regards,
>Ivor Lewis.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Bill Merrill on mon 6 aug 07
Ron,
I have seen bodies that were reduced from cone 016 through cone 10 and
the kiln oxidized for such a long time in cooling, the interior of the
clay body wasn't the customary grey(reduced iron) that is was orange
through. I wonder if the body needed more flux?
Bill
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Ron Roy
Sent: Monday, August 06, 2007 5:53 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: Oxidatiom and reduction at the end of a firing
Just to add something here I think is important.
If reduction is started too late - after a glaze has sealed over the
clay -
the clay will not be evenly reduced. You will see the effect when you
break
the ware - different colours of the body. The clay should be evenly
reduced
all the way through.
RR
>Without going into detail I was taught that reduction should not begin
>until after the clay commenced its maturing cycle but must happen
before
>the lowest melting point glaze ingredient started to fuse. The first
>instruction to ensure carbonaceous materials were removed by burning,
the
>second so that the reducing medium could diffuse into the glaze and
>complete the reduction chemistry.
>I was also taught that once glazes had fully matured it was difficult
for
>reducing gases to permeate into the fused surface and do further work,
>thought oxygen at high temperature could affect surface colour. This
may
>explain why I have had many pots that should have been copper red all
>round that had a green windward side and a red leeward side.
>The final point was that if I wished to change the grey colour of a
>reduced Iron bearing clay this could be achieved by allowing air to
invade
>the kiln between 800 and 700 deg C as the kiln cooled.
>Those observations that reduced glazes which have been reoxidised on
>cooling are brighter suggests something happening at the molecular
level.
>As one of my Physics Teachers would say, "Go back to First Principles".
>Best regards,
>Ivor Lewis.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
________________________________________________________________________
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Moderator of the list is Mel Jacobson who may be reached at
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John Britt on tue 7 aug 07
Ron,
I cannot believe that this is true.
What is the reason that a clay body =93should be evenly reduced all the way
through=94? And how is that possible?
Thanks,
John Britt
www.johnbrittpottery.com
On Mon, 6 Aug 2007 19:53:22 -0500, Ron Roy wrote:
>Just to add something here I think is important.
>
>If reduction is started too late - after a glaze has sealed over the
clay -
>the clay will not be evenly reduced. You will see the effect when you
break
>the ware - different colours of the body. The clay should be evenly
reduced
>all the way through.
>
>RR
Chuck Wagoner on tue 7 aug 07
>>What is the reason that a clay body "should be evenly reduced all the way
>>through"? And how is that possible?
As opposed to carbon coreing? I don't think he means that the reduction has
to be even throughout the firing cycle, but that the reduction of the
claybody needs to be "even throughout the clay body".
I like to start body reduction at around 010 for the clay, but that is just
what Dick Hay taught us at I.S.U. At least before the glaze starts to
sinter.
Speaking of "reduction", the CUBS have just been reduced with Soriano out
for who knows how long.(A month at least) Now that is not beautiful, well
come to think of it I guess it is if you are a Brewers fan. Wahhhhhh!
Chuck in very hot Rockville, IN.
Charles Todd Wagoner
North Vermillion Jr./Sr. High School Visual Art Dept.
Billie Creek Village Potter, Rockville, IN
Charter Member "Bald Headed Potters of America"
Home of the Peeler Ceramic Art Films
cwag@abcs.com
ctwagoner@cebridge.net
cwagoner@nvc.k12.in.us
http://www.abcs.com/cwag
http://www.nvc.k12.in.us
http://www.myspace.com/themuddoctor
Ron Roy on tue 7 aug 07
Hi Bill,
Yes - if a clay body is water tight it will only reoxidize on the surface -
it means you clay is not mature enough - I try to keep all stoneware
between 1 and 2% absorption.
The open body is probably why you are getting such good colour.
RR
>Ron,
>
>I have seen bodies that were reduced from cone 016 through cone 10 and
>the kiln oxidized for such a long time in cooling, the interior of the
>clay body wasn't the customary grey(reduced iron) that is was orange
>through. I wonder if the body needed more flux?
>
>Bill
>
>-----Original Message-----
>From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Ron Roy
>Sent: Monday, August 06, 2007 5:53 PM
>To: CLAYART@LSV.CERAMICS.ORG
>Subject: Re: Oxidatiom and reduction at the end of a firing
>
>Just to add something here I think is important.
>
>If reduction is started too late - after a glaze has sealed over the
>clay -
>the clay will not be evenly reduced. You will see the effect when you
>break
>the ware - different colours of the body. The clay should be evenly
>reduced
>all the way through.
>
>RR
>
>
>>Without going into detail I was taught that reduction should not begin
>>until after the clay commenced its maturing cycle but must happen
>before
>>the lowest melting point glaze ingredient started to fuse. The first
>>instruction to ensure carbonaceous materials were removed by burning,
>the
>>second so that the reducing medium could diffuse into the glaze and
>>complete the reduction chemistry.
>>I was also taught that once glazes had fully matured it was difficult
>for
>>reducing gases to permeate into the fused surface and do further work,
>>thought oxygen at high temperature could affect surface colour. This
>may
>>explain why I have had many pots that should have been copper red all
>>round that had a green windward side and a red leeward side.
>>The final point was that if I wished to change the grey colour of a
>>reduced Iron bearing clay this could be achieved by allowing air to
>invade
>>the kiln between 800 and 700 deg C as the kiln cooled.
>>Those observations that reduced glazes which have been reoxidised on
>>cooling are brighter suggests something happening at the molecular
>level.
>>As one of my Physics Teachers would say, "Go back to First Principles".
>>Best regards,
>>Ivor Lewis.
>
>Ron Roy
>RR#4
>15084 Little Lake Road
>Brighton, Ontario
>Canada
>K0K 1H0
>
>________________________________________________________________________
>______
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at
>melpots@pclink.com.
>
>______________________________________________________________________________
>Send postings to clayart@lsv.ceramics.org
>
>You may look at the archives for the list or change your subscription
>settings from http://www.ceramics.org/clayart/
>
>Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Ron Roy on tue 7 aug 07
Hi John,
I think we have had this conversation before -
If a clay body is not reduced to the same extent all the way through you
are then dealing with differently fired clay - laminated together - with
different absorption and expansions.
Why would anyone do that on purpose?
You would be building stresses into your ware and asking your glazes to
adapt to different clays all in the same pot.
If there is iron present then the body should be the same grey or black all
the way through with a thin skin of reoxidized clay if the body is properly
vitrified so as not to leak.
If it is not then you need to adjust your firing to make sure the clay is
properly reduced before the glazes seal over. The fault I see most often is
reoxidized clay due to slipping out of reduction before the clay is
vitrified - usually where there is no glaze.
RR
>Ron,
>
>I cannot believe that this is true.
>
>What is the reason that a clay body =93should be evenly reduced all the way
>through=94? And how is that possible?
>
>Thanks,
>
>John Britt
>www.johnbrittpottery.com
>
>
>On Mon, 6 Aug 2007 19:53:22 -0500, Ron Roy wrote:
>
>>Just to add something here I think is important.
>>
>>If reduction is started too late - after a glaze has sealed over the
>clay -
>>the clay will not be evenly reduced. You will see the effect when you
>break
>>the ware - different colours of the body. The clay should be evenly
>reduced
>>all the way through.
>>
>>RR
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
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