Jump to content

Recommended Posts

flowerdry    128

When starting something new, like a new form I haven't made before, I always assume it's going to involve lots of failure until I'm satisfied with the result.  But I don't think of my unsuccessful attempts as failures.  They're just points along the path to success, and I try to enjoy the journey.

 

Doris

Share this post


Link to post
Share on other sites
docweathers    79

Sometimes I have more fun solving glaze and throwing problems than creating pretty pots.  Once I get something to work well, I usually lose interest in it. I'm not inclined to reproduce that item, but then of course, hobbyist versus a production Potter.

 

Learning from failures requires extensive data collection so you can understand that caused the failures. No data, no learn. I have a database that allows me to take pictures of of everything I do after glazing and after firing, with extensive notes. When something goes wrong to this provides a lot of clues to solving the problem.

 

Lately, I've been running many hundreds of test tiles to try to get a better pallet of glazes. This approach is been invaluable in sorting out what works and what doesn't. Some days I think test tiles are my art.form. :mellow:  

Share this post


Link to post
Share on other sites
Norm Stuart    80

I'm far prouder of test tiles of glazes I've worked on than ceramic pieces I've made.  And usually it's my partner who made the test tile itself.

 

Solving a riddle is far sweeter than something which merely goes right.

 

Test tiles are an anticipation of things to come, while a finished piece is merely part of my past.

 

Sometimes I have more fun solving glaze and throwing problems than creating pretty pots.  Once I get something to work well, I usually lose interest in it. I'm not inclined to reproduce that item, but then of course, hobbyist versus a production Potter.

 

Learning from failures requires extensive data collection so you can understand that caused the failures. No data, no learn. I have a database that allows me to take pictures of of everything I do after glazing and after firing, with extensive notes. When something goes wrong to this provides a lot of clues to solving the problem.

 

Lately, I've been running many hundreds of test tiles to try to get a better pallet of glazes. This approach is been invaluable in sorting out what works and what doesn't. Some days I think test tiles are my art.form. :mellow:  

Share this post


Link to post
Share on other sites
ChenowethArts    461

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.  The kiln sitter had not cut off so my initial though was the dense load is just taking longer.  Finally, a look through the peeps revealed a much brighter heat color than my experience taught me and I decided to shut down the kiln.  The next day when everything was cool, 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.  The bisque was wayyyy over-fired.  So, back-to-basics: I make sure there is a visible cone at one peep hole, I promise to kick myself if I am silly enough to put wet stuff in the kiln, I will trust my instincts when firing times go beyond a reasonable time frame, and I will not be completely dependent on the old kiln sitter..

Share this post


Link to post
Share on other sites
Pres    896

Paul, I had nearly the same thing happen to me one firing in  the HS. We had reassembled the kiln after putting in a new floor, I had forgotten to check the kiln setter. Our setter was positioned over two sections. It seems the top section was shifted a little inward. This caused the cone to melt, but the setter tab to not fall.  I have always gotten used to checking kiln temp by heat color, and noticed that the kiln had hit yellow orange. Checked the setter, and sure enough at I touched it the tab dropped. At home here as I fire completely from cones checking heat color keeps me informed of the speed and temp of the kiln, a useful skill for any potter.

Share this post


Link to post
Share on other sites
Benzine    610

Wow Paul, I never even thought about that happening.  What are the odds of that piece getting stuck right where it needed to be, to cause that to happen?  Good thing you checked.

 

That's why I'm glad, the couple of cone sitter kilns I've used in my classrooms, had the timer shut off as well.  I knew the time it would take to get to the required cone, and set the timer accordingly.  Unless the timer failed, I couldn't over fire. 

 

Norm, you are very pro-controller.  I don't fault you for that, they are great.  I love the fact, that I can set my classroom kiln to heat at a consistent rate, and hold, to pre-heat my iffy student projects. 

Share this post


Link to post
Share on other sites
Babs    386

 

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.com/kilns/olympic_kilns/electro_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.

Share this post


Link to post
Share on other sites
Chris Campbell    1,088

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 ... : - )

Share this post


Link to post
Share on other sites
JBaymore    1,432

Air bubbles (or hollow cloesed forms) do not cause pieces to blow up.  It is ceramic myth #1.

 

If you do the math on the gas pressure laws over the temperatures involved versus the tensile strngth of clay materials...... it doesn't add up.

 

What causes the blow ups is trapped moisture inside the small "bubble" voids or inside the hollow forms.

 

It takes a surprising amount of time for the last water of formation to leave the interrior of "dry" clay when the outer surface layer has dried, thereby letting the clay platelets move together.... cuting off the eeasy pathways for moisture to reach the surface and evaporate.  Different clays bodies will exhibit this to different levels.

 

There are many people who make totally enclosed forms and fire them successfully.  I've demonstrated this in classes repeatedly.

 

You can fire totally enclose forms.  Just be CERTAIN that they are DRY.

 

best,

 

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

Share this post


Link to post
Share on other sites
Babs    386

 

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.

Share this post


Link to post
Share on other sites
Norm Stuart    80

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.

Share this post


Link to post
Share on other sites
Babs    386

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.

Share this post


Link to post
Share on other sites
Norm Stuart    80

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.

Share this post


Link to post
Share on other sites
Babs    386

 

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!

Share this post


Link to post
Share on other sites
JBaymore    1,432

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

Share this post


Link to post
Share on other sites
Chris Campbell    1,088

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.

Share this post


Link to post
Share on other sites
Babs    386

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.

Share this post


Link to post
Share on other sites
ChenowethArts    461

 

 

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.com/kilns/olympic_kilns/electro_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

Share this post


Link to post
Share on other sites
Babs    386

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

Share this post


Link to post
Share on other sites
JBaymore    1,432

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

Share this post


Link to post
Share on other sites
Norm Stuart    80

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

 

Share this post


Link to post
Share on other sites
Pres    896

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.

Share this post


Link to post
Share on other sites
bciskepottery    925

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. :)

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×