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PeerieMoose

Can I Leave Newspaper Inside My Sculpture When Firing?

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Hi!!
 
I have just finished a sculpture of a baby using smooth red clay.  
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This is my third clay sculpture, but first without a teacher to guide me.
 
With my previous sculptures, it was easier to remove the armatures.. there were less detailed areas which made it less traumatic to cut open/join back together.  I was also far less particular about my sculptures then as can be seen by the fact I removed the armatures far too early.

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Is it okay for me to leave the paper inside when I fire it?
 
Also, how slowly should I dry it to make sure fingers, toes and ears don't crack?

 

Any other advice?

 

Thanks in advance :)

glazenerd and Sputty like this

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Dry slowly for as long as you can.

 

Then fire slowly, particularly up to and around boiling point of water - 100c.    

 

I fire at 30deg per hour till 100c, hold for 20 minutes, then normal rate up to bisque temperature.  Frequently put not-dry stuff into kiln on a Wednesday lunchtime, programme kiln to switch on on Friday afternoon and haven't blown anything up yet.

 

Excellent work, really life-like, but a bit spooky too.

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very nice work.  assume your instructor has told you to leave a hole somewhere for air to escape.  as long as you do not have lots of paper inside, go ahead and fire it.

 

leave the kiln room during the early part of the firing.

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Thank you all very much!! That has put my mind a little more at ease.

 

How do I make sure that it's drying slowly enough? and how slowly is slowly? I had in my head about 3 weeks  :unsure:

 

assume your instructor has told you to leave a hole somewhere for air to escape.

Thank you for reminding me to make a hole somewhere.. I had forgotten to!

 

 

Excellent work, really life-like, but a bit spooky too.

Spooky, creepy and unnerving is what I aim for! I've also taken note of your firing process, thank you.

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Thank you all very much!! That has put my mind a little more at ease.

 

How do I make sure that it's drying slowly enough? and how slowly is slowly? I had in my head about 3 weeks  :unsure:

 

assume your instructor has told you to leave a hole somewhere for air to escape.

Thank you for reminding me to make a hole somewhere.. I had forgotten to!

 

 

Excellent work, really life-like, but a bit spooky too.

Spooky, creepy and unnerving is what I aim for! I've also taken note of your firing process, thank you.

 

 

The hole is not for air, it's for moisture to escape during the slow drying process.  Air doesn't expand any more than clay does during firing, but water expands rapidly when boiling, and it is the escaping steam that will blow your sculpture apart.  When clay dries, it forms a crust on the surface, which stops the moisture deeper within from escaping so easily.  Enclosed spaces in pots don't dry, however long you leave them.  I made a hollow ball and left it in the greenhouse for months, when I eventually broke it open, the inside was not as dry as the outside.

 

 

Creepy and unnerving are better descriptions, but I didn't want to appear rude on your first posting. :-) 

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The hole is not for air, it's for moisture to escape during the slow drying process.  Air doesn't expand any more than clay does during firing, but water expands rapidly when boiling, and it is the escaping steam that will blow your sculpture apart.  When clay dries, it forms a crust on the surface, which stops the moisture deeper within from escaping so easily.  Enclosed spaces in pots don't dry, however long you leave them.  I made a hollow ball and left it in the greenhouse for months, when I eventually broke it open, the inside was not as dry as the outside.

 

 

 

 

Creepy and unnerving are better descriptions, but I didn't want to appear rude on your first posting. :-) 

 

Thanks for explaining this.. I do find the whole air/moisture/explosions thing very confusing.  So much conflicting advice online, in books, etc.

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Regarding water and drying, one must consider not only the 2 stages of water exiting the clay, but the thickness of the clay itself in order to allow the water to exit. The first stage of water exiting the clay is the obvious free "wet" water. This is a concern because water changes from liquid state to gaseous state at 212F/100C with a tremendous release of energy as it changes from water to steam. The clay wares will explode. Nothing new there. But the thickness of the ware will change the probability and timing of such an explosion. Extremely thick pieces may be dry on the outside but still damp deep in the interior. Simultaneously, it will take some time for the heat to penetrate to the interior, which means that the remaining water in the center will reach the explosion point long after nominal temperature in the kiln has passed the boiling point. Thus, it is imperative to heat the kiln very slowly and hold at 190F/90C for a long time to force the wet water out of the interior of the clay.

 

The second stage of water exit occurs around 900F/475C when the raw clay molecule is hot enough to reorganize into the conventional ceramic oxides of silica and alumina. In pure form, the raw clay molecule is Al2Si2O5(OH)4. But when it is heated, the molecular bonds reorganize into one alumina oxide molecule Al2O3, two silica oxide molecules SiO2, and the excess 4 H atoms and 2 O atoms form 2 new water molecules. These new water molecules are already steam, but they must get out somehow. The surface of the clay is still somewhat porous and it can escape. But as the temperature increases, the porosity decreases, making it more difficult for the new steam to escape. Just as before with the temperature differential between the surface and the interior of a very thick piece causing the interior wet water to explode long after the surface of the piece has dried, it is possible at this stage that the surface of the clay will be sintering and sealing over just as new steam is being generated deep inside. When this happens, large chucks spall off. It will not be a violent explosion with shards and dust thrown throughout the kiln, but simply big chunks falling off.

With sculptures, the thickness of your work matters greatly.

 

Pugaboo likes this

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Very nice sculptures. I would leave the lid open about 4" and let the smoke out. Go slowly for a few hours until the smoke is gone. Then shut the lid. Have an exhaust system in place to get the smoke out of the kiln area and outside.Then go slowly as you continue firing.Are there holes for smoke to escape in the scupltures?

 

Marcia

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Regarding water and drying, one must consider not only the 2 stages of water exiting the clay, but the thickness of the clay itself in order to allow the water to exit. The first stage of water exiting the clay is the obvious free "wet" water. This is a concern because water changes from liquid state to gaseous state at 212F/100C with a tremendous release of energy as it changes from water to steam. The clay wares will explode. Nothing new there. But the thickness of the ware will change the probability and timing of such an explosion. Extremely thick pieces may be dry on the outside but still damp deep in the interior. Simultaneously, it will take some time for the heat to penetrate to the interior, which means that the remaining water in the center will reach the explosion point long after nominal temperature in the kiln has passed the boiling point. Thus, it is imperative to heat the kiln very slowly and hold at 190F/90C for a long time to force the wet water out of the interior of the clay.

 

The second stage of water exit occurs around 900F/475C when the raw clay molecule is hot enough to reorganize into the conventional ceramic oxides of silica and alumina. In pure form, the raw clay molecule is Al2Si2O5(OH)4. But when it is heated, the molecular bonds reorganize into one alumina oxide molecule Al2O3, two silica oxide molecules SiO2, and the excess 4 H atoms and 2 O atoms form 2 new water molecules. These new water molecules are already steam, but they must get out somehow. The surface of the clay is still somewhat porous and it can escape. But as the temperature increases, the porosity decreases, making it more difficult for the new steam to escape. Just as before with the temperature differential between the surface and the interior of a very thick piece causing the interior wet water to explode long after the surface of the piece has dried, it is possible at this stage that the surface of the clay will be sintering and sealing over just as new steam is being generated deep inside. When this happens, large chucks spall off. It will not be a violent explosion with shards and dust thrown throughout the kiln, but simply big chunks falling off.

 

With sculptures, the thickness of your work matters greatly.

 

Thank you for explaining this further.  I was aware of the the first stage, but not the second!! 

 

 

Very nice sculptures. I would leave the lid open about 4" and let the smoke out. Go slowly for a few hours until the smoke is gone. Then shut the lid. Have an exhaust system in place to get the smoke out of the kiln area and outside.Then go slowly as you continue firing.Are there holes for smoke to escape in the scupltures?

 

Marcia

I have 3 holes in the body, 3 in the head and 1 in each of the limbs.. about 2-3mm wide

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Very nice sculptures. I would leave the lid open about 4" and let the smoke out. Go slowly for a few hours until the smoke is gone. Then shut the lid. Have an exhaust system in place to get the smoke out of the kiln area and outside.Then go slowly as you continue firing.Are there holes for smoke to escape in the scupltures?

 

Marcia

 

All of the kilns I've fired, have a contact switch, and won't fire if the lid/door isn't properly shut.  I wonder if this is a UK safety feature?

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Very nice sculptures. I would leave the lid open about 4" and let the smoke out. Go slowly for a few hours until the smoke is gone. Then shut the lid. Have an exhaust system in place to get the smoke out of the kiln area and outside.Then go slowly as you continue firing.Are there holes for smoke to escape in the scupltures?

 

Marcia

 

All of the kilns I've fired, have a contact switch, and won't fire if the lid/door isn't properly shut.  I wonder if this is a UK safety feature?

 

I'm going to check the one at the college on Monday.. they seem pretty reluctant to let me get to know this kiln and how it works.

I haven't been involved in any of the firing processes up to now, other than being shown how to open the door (...yay  <_<)

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Chilly I have a heavyish bolt I drop into the hole which depresses the lever, usually activated by the door/lid. This allows me to gave the lid/door ajar to let any steam escape....

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