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#1 Natas Setiabudhi

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Posted 30 July 2012 - 11:29 AM

Hi guys
About 6 months, my bowl with sig has been displaying in my workshop. But there is oddities when saw the surface body. At the first time, the surface was red shine. But now the surface change into dull red and has black spots. Why this happens?
I attach the following bowl. Before (mangkok sig) and after (picture 199). I really appreciate for all comments.

Attached Files


Natas Setiabudhi
Kupu Ceramic Studio, Indonesia
www.butterflyceramic.blogspot.com

#2 trina

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Posted 30 July 2012 - 01:13 PM

Hello,

Is this a clay body that you normally use with that sig. I have had this happen to me when I combined a very groggy crude terra cotta with sig. Not sure though.... T

#3 Natas Setiabudhi

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Posted 31 July 2012 - 11:01 AM

Hello,

Is this a clay body that you normally use with that sig. I have had this happen to me when I combined a very groggy crude terra cotta with sig. Not sure though.... T



Hi
Thanks for replying. I used local red earthenware. The clay is a bit coarse and contain granules. May be you are right, it was influenced by coarse matter. I thought, the blackish like mildew.


Natas Setiabudhi
Kupu Ceramic Studio, Indonesia
www.butterflyceramic.blogspot.com

#4 trina

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Posted 31 July 2012 - 02:01 PM


Hello,

Is this a clay body that you normally use with that sig. I have had this happen to me when I combined a very groggy crude terra cotta with sig. Not sure though.... T



Hi
Thanks for replying. I used local red earthenware. The clay is a bit coarse and contain granules. May be you are right, it was influenced by coarse matter. I thought, the blackish like mildew.



Hi again,
What temp are you firing at? I will take a picture of my pot with the same problem, to compare. T

#5 Natas Setiabudhi

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Posted 31 July 2012 - 05:30 PM



Hello,

Is this a clay body that you normally use with that sig. I have had this happen to me when I combined a very groggy crude terra cotta with sig. Not sure though.... T



Hi
Thanks for replying. I used local red earthenware. The clay is a bit coarse and contain granules. May be you are right, it was influenced by coarse matter. I thought, the blackish like mildew.



Hi again,
What temp are you firing at? I will take a picture of my pot with the same problem, to compare. T


Hi
The temperature was 950C (1742F).Posted Image


Natas Setiabudhi
Kupu Ceramic Studio, Indonesia
www.butterflyceramic.blogspot.com

#6 trina

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Posted 05 August 2012 - 03:03 AM




Hello,

Is this a clay body that you normally use with that sig. I have had this happen to me when I combined a very groggy crude terra cotta with sig. Not sure though.... T



Hi
Thanks for replying. I used local red earthenware. The clay is a bit coarse and contain granules. May be you are right, it was influenced by coarse matter. I thought, the blackish like mildew.



I am not an expert, but that seems a little low to me. I normally start a low fire terra cotta off at 980C - 1050 depending on the finish. Have you had this problem with other pieces? I haven't forgot the picture, just have been busy last few days. T

Hi again,
What temp are you firing at? I will take a picture of my pot with the same problem, to compare. T


Hi
The temperature was 950C (1742F).Posted Image




#7 trina

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Posted 05 August 2012 - 03:04 AM

I am not an expert, but that seems a little low to me. I normally start a low fire terra cotta off at 980C - 1050 depending on the finish. Have you had this problem with other pieces? I haven't forgot the picture, just have been busy last few days. T

#8 Natas Setiabudhi

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Posted 05 August 2012 - 11:19 AM

I am not an expert, but that seems a little low to me. I normally start a low fire terra cotta off at 980C - 1050 depending on the finish. Have you had this problem with other pieces? I haven't forgot the picture, just have been busy last few days. T


Hi
Ya all my pot about 6 had the same problem (same clay). The body surface became like the picture that I have given. But I assume the cause is coarse material in the clay not the temperature, just you said in the first discussion. But I don't know, may be the temperature factor could be..


Natas Setiabudhi
Kupu Ceramic Studio, Indonesia
www.butterflyceramic.blogspot.com

#9 ratdog

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Posted 06 August 2012 - 07:27 AM


I am not an expert, but that seems a little low to me. I normally start a low fire terra cotta off at 980C - 1050 depending on the finish. Have you had this problem with other pieces? I haven't forgot the picture, just have been busy last few days. T


Hi
Ya all my pot about 6 had the same problem (same clay). The body surface became like the picture that I have given. But I assume the cause is coarse material in the clay not the temperature, just you said in the first discussion. But I don't know, may be the temperature factor could be..




i agree increese temp ...cone 04 might soak 1 hr. give dark stuff time to melt better so water dont oxidise iron. im no expert but remove the hevey big stuff my self.

#10 Natas Setiabudhi

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Posted 06 August 2012 - 11:15 AM



I am not an expert, but that seems a little low to me. I normally start a low fire terra cotta off at 980C - 1050 depending on the finish. Have you had this problem with other pieces? I haven't forgot the picture, just have been busy last few days. T


Hi
Ya all my pot about 6 had the same problem (same clay). The body surface became like the picture that I have given. But I assume the cause is coarse material in the clay not the temperature, just you said in the first discussion. But I don't know, may be the temperature factor could be..




i agree increese temp ...cone 04 might soak 1 hr. give dark stuff time to melt better so water dont oxidise iron. im no expert but remove the hevey big stuff my self.


Thank you for your replying, I really appreciate. Ya I will try again to make a new one and fire more higher.
Natas Setiabudhi
Kupu Ceramic Studio, Indonesia
www.butterflyceramic.blogspot.com




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