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#61 Babs

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Posted 23 January 2014 - 01:57 AM

 

You probably watched the same video I did of Mrs. Zhang, of Jingdezhen, making a tea pot with clay coils.

 

She made a coil

 

 

I have seen a potter whose handles are hollow with no air hole made, so how does that work??

 

No Norman, it was an American potter who formed handles by rolling out her clay and forming it into tubes which she then shaped and sealed the ends as she attached them onto various pots, no pinholes in the process.



#62 Norm Stuart

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Posted 23 January 2014 - 02:20 AM

The clay had best be pretty thin or there will be a radical restructuring of the handles right around 1,050 F.

You probably watched the same video I did of Mrs. Zhang, of Jingdezhen, making a tea pot with clay coils.


I have seen a potter whose handles are hollow with no air hole made, so how does that work??

No Norm, it was an American potter who formed handles by rolling out her clay and forming it into tubes which she then shaped and sealed the ends as she attached them onto various pots, no pinholes in the process.



#63 Babs

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Posted 23 January 2014 - 02:47 AM

Don't know about that but also when teaching, the odd student would make a piece with no airholes just to see!. Because I fired nothing that resembled anything damp,+the kiln on low o' night, then gradually rising over the next day ,he piece would survive much to the amazement of the student, who waited to see the effects of such a pot. Usually found this out because the student would be extra keen to see their wares, andtelling their friends about it. I presumed it was the fact that the piece was totally dry, JB has confirmed  +the reasons why.



#64 Norm Stuart

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Posted 23 January 2014 - 03:11 AM

Just bear in mind that totally dry clay gives off 12% of its weight as superheated steam between 1,000 F (538 C) and 1,100 F (593 C).

 

Our kiln increases the heat over that range at 100 F per hour (55 C per hour) and anything too thick just doesn't survive.

 

If you ramp the temperature more slowly over that range you may be able to fire thicker pieces.

 

Clay bodies made with more grog and or sand and less clay or kaolin will also be more forgiving.

 

Don't know about that but also when teaching, the odd student would make a piece with no airholes just to see!. Because I fired nothing that resembled anything damp,+the kiln on low o' night, then gradually rising over the next day ,he piece would survive much to the amazement of the student, who waited to see the effects of such a pot. Usually found this out because the student would be extra keen to see their wares, andtelling their friends about it. I presumed it was the fact that the piece was totally dry, JB has confirmed  +the reasons why.



#65 Babs

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Posted 23 January 2014 - 03:45 AM

 

Just bear in mind that totally dry clay gives off 12% of its weight as superheated steam between 1,000 F (538 C) and 1,100 F (593 C).

 

Our kiln increases the heat over that range at 100 F per hour (55 C per hour) and anything too thick just doesn't survive.

 

If you ramp the temperature more slowly over that range you may be able to fire thicker pieces.

 

Clay bodies made with more grog and or sand and less clay or kaolin will also be more forgiving.

 

Don't know about that but also when teaching, the odd student would make a piece with no airholes just to see!. Because I fired nothing that resembled anything damp,+the kiln on low o' night, then gradually rising over the next day ,he piece would survive much to the amazement of the student, who waited to see the effects of such a pot. Usually found this out because the student would be extra keen to see their wares, andtelling their friends about it. I presumed it was the fact that the piece was totally dry, JB has confirmed  +the reasons why.

 

Like everything, know what works with the stuff you use. Firing student work made me very cautious with different thicknesses of clay in each firing.  My own stuff I test its strengths from time to time but clay is an unforgiving medium. Very humbling..There's another potter Scottish who makes floating rocks! She sets them fre in lochs and seas around Scotland. No pinholes in them!



#66 JBaymore

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Posted 23 January 2014 - 10:31 AM

Val Cushing is famous for his torroidal (hollow tube) rims and feet on pieces.  Many relativelty larger scale.  No holes in them.

 

The Kaolin/meta kaolin conversion does evolve water molecules, but it is not sudden like alpha/beta quartz inversion.  Plus it also depends on the thermal lag of the movement of heat energy through the walls of a piece, with the surface of the ware giving off the bonded water before the materials further inside the wall.  Then you have the gas permeability qualities of the (almost) bisqued clay to the water vapor molecules.... and the relative strength of the body to withstand the potential pressure generated in the process. 

 

Know your materials and what happens to them in your particular process. 

 

I have a handout I use in my ceramic material classes titled .......

 

"The Science Behind the Art  .....or....... You Thought You Were In Art School And Didn't Need That Science Stuff".  ;)

 

best,

 

.................john


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#67 Chris Campbell

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Posted 23 January 2014 - 11:32 AM

Floating rocks! I love this idea ... Brilliant.
I make rocks of all shapes and sizes but never thought about the possibilities of having them float. I have six large bisqued ones sitting around and I am seriously thinking of being a total art thief/copycat ... Is there a lake near Milwaukee I can float them in during NCECA? Or maybe just leave them on the ice and wait for the thaw.

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#68 Babs

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Posted 23 January 2014 - 05:26 PM

Floating rocks! I love this idea ... Brilliant.
I make rocks of all shapes and sizes but never thought about the possibilities of having them float. I have six large bisqued ones sitting around and I am seriously thinking of being a total art thief/copycat ... Is there a lake near Milwaukee I can float them in during NCECA? Or maybe just leave them on the ice and wait for the thaw.

You could go out onto your lake, thick with ice, use your pots as curling stones and leave them there to float around til next year! The potter's book is called "Floating stones", can't remember her name.



#69 ChenowethArts

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Posted 24 January 2014 - 10:17 AM

 

 

Even adding a long pre-heat before a bisque with a computer controller we still have to be concerned about the bowl which has been thrown with air-bubbles inclusions.  It may pack the punch of a grenade, but at least the fragments can't interfere with the firing controller.

 

The result is people at our studio have become pretty good at catching air bubble pots as they're being thrown, so get tossed before they get to the "To be Bisqued" shelf.

 

But you still might appreciate swapping out your kiln sitter for a V6-CF.  http://www.clay-king...tro_sitter.html

 

I have filed this failure under the category "Trust Your Instincts"...and "Back-up your kiln sitter".  I was pushing a bisque firing back in November to have things ready for a holiday sale...and by 'push', I mean I placed a few items in the bisque kiln that were not completely dry...ok, full disclosure, they were still pretty damp.  I never heard the 'pop' of an exploding pot but did notice that the firing seemed to be taking much longer than usual. 

 

I opened the lid to discover that one of those 'damp' pots did explode AND lodged a small shard in the kiln sitter bracket preventing the shut-off bar from dropping when the cone softened.

 

I have seen a potter whose handles are hollow with no air hole made, so how does that work?? Or is the exploding pot not because of trapped air but dampness? Thickness of piece with air trapped may be part of the scenario.

 

 

Thanks all for the feedback.. I know that I am over due for upgrading my electric kiln and know the benefits of an electronic controller from experience at school... I'll be talking with Santa about that this year:)

 

As far as air pockets and moisture..and which is more explosive?  Moisture is a killer.  Even the groggiest of clays will do nasty things if there is moisture trapped somewhere. A long pre-heat for that large piece that you have worked on for dayyyyys may cost you a bit more in electricity, but it is good insurance if it means eliminating moisture..  Air pockets in dense, tight-particled clay can do nasty things as well and I can attest to that.  Even the tiniest hole to vent an air bubble or a hollow attachment is worth it.  Trapped air in groggy clays may be a little less likely to explode, but I'm still and advocate for getting moisture AND trapped air out of everything!

 

I think  thickness and uneven-thickness is a related discussion, but I make a distinction between exploding (due to moisture and air)  and cracking (from unevenness or extra thickness).

 

My  2 cents worth,

Paul


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#70 Babs

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Posted 24 January 2014 - 05:59 PM

What about the guys who put ware straight off their wheels into a sealed kiln, no explosions, very wet ware??



#71 JBaymore

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Posted 24 January 2014 - 08:16 PM

What about the guys who put ware straight off their wheels into a sealed kiln, no explosions, very wet ware??

 

Yup ... it works.  For the same reason that the industrial dryers work so well.  I've demoed this in classes.  It is about the PHYSICALwater of formation here ... not the chemically combined water (which is almost NEVER an issue in causing problems unless you are firing very fast relative to the thickness of the wares).

 

The "trick" here is that the partial pressure of water vapor in the closed kiln is such that as the temperatrure is raised slightly, the clay walls are warmed evenly throughout.  So there is .... let's call it "motivation" for the water in the clay to start heading toward evaporating.  But the atmosphere will not let it evaporate quickly.... because the armosphere is holding most all of the water vapor it can hold. So now you have hot clay (containing water) waiting for a chance to dry out.

 

Because the OUTER SURFACE of the clay body does not dry first........ thereby cutting off the pores in the clay body between the clay platelets separated by layers of water that allow that water transport to the surface........ the water can qmigrate from the inside toweard the outside evenly.

 

Then the kiln is slowly allowed to have circulation to slowly drop the partial pressure of water vapor in the atmosphere.... with the clay wares at somewhat elevated temperatures.... driving rapid and even drying through the wall sections.

 

Industrial driers have controlled humidity, temperature, and air circulation.  You program in the changes.  Work like a charm. 

 

best,

 

................john


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#72 Norm Stuart

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Posted 25 January 2014 - 01:47 AM

Before finally eliminating clay from his formulations for architectural ceramic sculptures, Alexandre Bigot initially used gas kilns which would fire thick pieces at extremely slow rate over a period of weeks.  Even in the 1880s this proved to be too costly and still resulted in too many failure - so he resorted to already bisqued raw ingredients with a binder, with the shapes formed in hydraulic presses.

 

You see his readily identifiable buildings all over Europe.

 

What about the guys who put ware straight off their wheels into a sealed kiln, no explosions, very wet ware??

 

Yup ... it works.  For the same reason that the industrial dryers work so well.  I've demoed this in classes.  It is about the PHYSICALwater of formation here ... not the chemically combined water (which is almost NEVER an issue in causing problems unless you are firing very fast relative to the thickness of the wares).

 

The "trick" here is that the partial pressure of water vapor in the closed kiln is such that as the temperatrure is raised slightly, the clay walls are warmed evenly throughout.  So there is .... let's call it "motivation" for the water in the clay to start heading toward evaporating.  But the atmosphere will not let it evaporate quickly.... because the armosphere is holding most all of the water vapor it can hold. So now you have hot clay (containing water) waiting for a chance to dry out.

 

Because the OUTER SURFACE of the clay body does not dry first........ thereby cutting off the pores in the clay body between the clay platelets separated by layers of water that allow that water transport to the surface........ the water can qmigrate from the inside toweard the outside evenly.

 

Then the kiln is slowly allowed to have circulation to slowly drop the partial pressure of water vapor in the atmosphere.... with the clay wares at somewhat elevated temperatures.... driving rapid and even drying through the wall sections.

 

Industrial driers have controlled humidity, temperature, and air circulation.  You program in the changes.  Work like a charm. 

 

best,

 

................john

 



#73 Babs

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Posted 25 January 2014 - 03:51 AM

Yip, there's more than one way to skin a cat!



#74 Pres

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Posted 25 January 2014 - 10:53 AM

In my HS classroom I had two downdraft industrial blowers. These tables with gigantic fans and four walls of filters were purchase for me to use as air filtration systems along with the large wall mounted device in the room. When I taught week long summer classes in Ceramics I would use these to force dry pieces by students ranging from 6-13. These were mostly slab constructions and coil constructions. I would force the last load on a Wednesday when they finished their pots by putting everything on the blowers for 3 hrs. Load the kiln, fire slow to 1100F. then finish up. Next morning all pieces were glazed, loaded and fired for Friday class. The downdraft blower would take a 3/8" slab 12'X12" to bone dry in 45 minutes!

 

Over the years of firing, and seeing blown ware on occasion, I learned that air bubbles had nothing to do with explosions. Looking at the shards from a blown pot, 90% of the time they would be sharp, small, and kind of following some sort of striation or grain in the piece. Very few times would one find a smooth edge, or pocket indicating an air pocket. I made certain to check closely how the pieces were, how far they would travel, and the type of shard they would leave.  It became easy to assume in the end that the only reason for a blow up in the kiln was excess moisture, either from the piece not being dry or not coming up to 1100F. slow enough. For these reasons, I candled student work carefully, and also watched my rate of climb with the manual kilns that I used.

 

I used to do a project years ago where I would have students cover river rocks with slabs sealed tight, then remove the rock reassemble the slab and cut out an opening for a container adding a decorative handle or sculptural top. On occasion students insisted on not adding an opening because they wanted the rock form as sculpture. I went along, fired the pieces and they survived easily. I had not bought into the blow up of trapped air myth.


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#75 bciskepottery

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Posted 25 January 2014 - 11:10 AM

Is there a lake near Milwaukee I can float them in during NCECA? Or maybe just leave them on the ice and wait for the thaw.


Last time I was there, Milwaukee was near a lake; I believe it was called Lake Michigan or something like that. Locals seemed to think it was some type of "great" lake. :)

#76 Chris Campbell

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Posted 25 January 2014 - 11:44 AM

Can you tell geography is not my strong suit?? It is especially not a good thing when planning flights with stop overs. I have flown some weird routes .... and not to gain air miles. : - )

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#77 Babs

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Posted 26 January 2014 - 05:34 AM

Can you tell geography is not my strong suit?? It is especially not a good thing when planning flights with stop overs. I have flown some weird routes .... and not to gain air miles. : - )

Now I know why you leave a trail of rocks around the planet!! You may just be able to find your way back home! Don't follow the floating ones.



#78 Chris Campbell

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Posted 08 February 2014 - 12:42 PM

Norm ... I wish you had done a control piece with no holes in it.
I don't always remember to put holes in closed forms but am very patient with my drying ... nothing fired til bone dry and I don't have explosions. This is with stoneware bodies, not the porcelain. I would not recommend doing it but I sometimes forget.

Of course the dominant fact is how much you care about the piece or if you need the whole kiln load of work for a show ... : - )

 

OK ... so I found the rocks (without holes) I wanted to fire so they could float in the lake ... four were bone dry and warm in the house and four were out in the unheated garage ... they felt damp.

Sooooo ..... in  my eternal quest to find answers with the least possible control or even deep thought I decided to bisque fire them all and see what happened. :ph34r:

Now, I wish I had put a hole in one of the damp ones to see if it made any difference but like I said, not much thought here.

I did however put up barriers to protect the rest of my full kiln load ...

Can you guess which rocks were dry and which were damp?? :rolleyes:

This is posted with no attempt to convince anyone else to try it on something they really care about. As your Mom would say, just because Chris jumps in the lake doesn't mean you should!

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#79 Babs

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Posted 08 February 2014 - 06:07 PM

Did you put 8 rocks in all up?? Looks like 4 survived .Did you know which ones came from the garage? SOrry shouldn't have asked that question.

Hey don't be tough on yourself you were in the throes of grasping floc and defloc! Things should have be easy after that! Life is just not fair..

I'm with your Mum on this one.

Remebemr to vacuum your element grooves :D



#80 Chris Campbell

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Posted 08 February 2014 - 06:32 PM

The kiln is already vacuumed ... all wares unloaded ... nothing damaged but the damp rocks.
I had a super heavy thick rock in the garage, but even I was not brave enough to fire it ...
Would have taken out the kiln if it had blown ... : - )

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