Jump to content
Sign in to follow this  
MMead

Bisque Blowouts

Recommended Posts

I did some searching but strangely didn't find info regarding my issue.

 

Im a newbie pottery of 3years, created my own studio two years ago.  My teacher said she couldn't teach me more and I went to apprentice with a production potter.  In my opinion my skill is good for only 3yrs but still has far far to go (I can throw shapes I choose and I can throw at a decent rate of pots/hour)

 

I have done several raw firings in a borrowed kiln and had few if any failures over the last year.  Having moved house I am sharing a kiln with a friend now.  She bisques and then glaze fires.  She fired some of my items when I very first started pottery.    My items blew up - I put it down to them not being dry and thickness issues etc.  During my year with a kiln to myself I had no breakage no blow-outs and with glaze testing I had nothing sticking to shelves even with raw firing - I'm as meticulous as possible.  I use witness cones etc.

 

Now with a lot of practice my pieces are more uniform.  Not having access to a kiln I decided to fire with her again and try to grit the bisque/glaze routine.  Strangely nearly every bowl was either reduced to rubble (literally a pile nothing recognizable) or the whole base was blown out.  The pots where dry (there was a moist day the day before the firing) my large bowl was fine.  Some of the bowls were fine.  My friend is the opposite of me and uses no cones, I'm not even sure she every peeps through her peep hole.

 

My question is this - had the bowls simply blown out at the base I would believe it's due to dampness.  What I'm confused at are the piles of rubble.  I've never heard of such a thing.  This leads me to wonder if perhaps the firing was to fast.  What about air bubbles - the clay we access has changed considerably but they factory is VERY private about what's in the clay the content etc.  I am very much wanting to put cones in her kiln and ask if I can camp there for the next firing.  I think she'd be offended as she never has a problem with her own items.

 

I'm seriously doubting myself now and am finding a more advanced teacher than the one I originally started with.  One so my techniques can be checked and two for the firing. 

Share this post


Link to post
Share on other sites

Perhaps discuss her firing schedules, if you have not had this problem with  other wares fired in different kilns then it looks like she is using a very different firing schedule which her clay can withstand and yours cannot.

Do I misunderstand.... are you raw glazing? If so is she thinking your ware can stand up to a pre bisque ware glaze firing schedule?? It wont.

Maybe a bit more info.. gas kiln or electric,  where your pots are placed in the kiln. Size of pots in comparison to hers

If you approach your friend and ask if you can be present to learn about bisque firing etc, and not load the placing of cones etc as a direct hit at her disastrous firing of your pots but of that of you learning, then sh e may  not be on the defensive. Let's face it you would not want to continue losing every pot you have made blow up in the kiln with no feedback.

Share this post


Link to post
Share on other sites

Was there anything different about your work that survived and stuff that didn't? 

 

I agree about the firing possibly being too fast. Even though the work is dry there is still water in there. Going too quick through water turning to steam will turn your pots to rubble. Stay around for the first hour or so and you should hear it pop. I am surprised nobody has before.

 

Could be something else but that is the best place to start.

Share this post


Link to post
Share on other sites

you say " the clay we access has changed considerably but they factory is VERY private about what's in the clay the content etc." Are you both using the same clay?

What clay is she using?

you say "Not having access to a kiln I decided to fire with her again and try to grit the bisque/glaze routine." So these pieces of yours were bisqued?

 

Marcia

Share this post


Link to post
Share on other sites

Seems like the firing is too fast.   

 

Did your work blow up in a bisque firing or were you trying to raw fire your work in the glaze firing of her bisque ware?  If the latter, that firing schedule is too fast - your pots need to go through a slow bisque firing.   If you continue to fire with her, she will need to adjust her firing schedule to accommodate your clay's requirements.  If she is unwilling to change her schedule, maybe its possible for you to rent the kiln from her and do a full load with only your work.  

 

-SD

Share this post


Link to post
Share on other sites

I do apologize I seem to have been confusing.  Thank you all so much for your input and the questions.  It reminds me how important every detail is and how wonderful community is.  I tried to answer all the questions throughly and clear up the confusion.

 

I was not firing raw here in this experience of a bisque fire.  My Raw firing was done all of last year.

 

My friend does the two fire process so I was following the two fire process and hoping to talk her into a raw fire at a later time.  Electric kiln.  I had a few pots at each level and several were of the same size and shapes. 

 

I did fire several different things with her.  Two different types.  What survived was the  Large recycled clay work.  What exploded was the "first time" high fire white stoneware. Only one or two of these survived and I'm curious if they will survive the glaze firing.

 

I love that y'all are like me in regarding firing but my friend as I've said is different.  She turns her kiln on and follows the "after two hours turn to setting 2"  after two hours turn to setting 3" etc - I don't think she is concerned with temps except the top temp.  She sent me a note that from Noon to 330pm the kiln had reach 600C / 1112F  I've not found my notes but I'm pretty sure this is too fast?

 

Thank you again for all the questions and help.  I am going to ask her regarding cones for a next firing (especially if we do glaze using my own made glazes - I've made for bisque and raw so I have this flexibility as I never knew what kiln access I would have).  

Share this post


Link to post
Share on other sites

Firing too fast. I put my kilns on low for 2 hours, then medium for an hour then all switches on high. Your rate of temperature climb should be 100 degrees per hour. Should take 8 hours to fire a bisque give or take.

Is she using a computerized kiln? Maybe adjust the rate of climb.

Funny that the recycled clay didn't explode and the new stuff did.

TJR.

Share this post


Link to post
Share on other sites

Candling would probably solve the problem. Crack the kiln lid and set the bottom element to low overnight. If it is. Digital controller, there are candling programs.

 

In my classroom, with the iffy nature of student work, my bisque program takes 12-15 hours. Even then, there can still be issues.

Share this post


Link to post
Share on other sites

Firing too fast. I put my kilns on low for 2 hours, then medium for an hour then all switches on high. Your rate of temperature climb should be 100 degrees per hour. Should take 8 hours to fire a bisque give or take.

Is she using a computerized kiln? Maybe adjust the rate of climb.

Funny that the recycled clay didn't explode and the new stuff did.

TJR.

Funny you say that - when I did my  short apprenticeship with a production potter he taught me to add bentonite to my recycled clay.  Maybe that's what did the trick? 

Share this post


Link to post
Share on other sites

To solve this I think you are going to have to do it in at least two steps.

 

One is to offer to pay for one kiln load that you would fire according to your preferences.

If the items blow up or disintegrate with you doing the firings ... then go to your clay to look for answers.

 

Trying to change both at once is just going to confuse things and string out the whole process.

Share this post


Link to post
Share on other sites

The easiest solution would be to ask your friend to email you the firing schedule, then post it here. That way we could know what was going on and help you solve the issue. 

 

I will get the firing schedule.  My pride has now calmed a bit and it seems from this thread that it's also about drying my pots further.  I would very much appreciate some help with the firing schedule.  She has a VERY old kiln - nothing computerized.  I've been given a Kiln that may be even older and doesn't even have a thermocoupler.  I'm having the people out in the week to try and see if it's worth fixing.

 

Thank you all again very much.  I'm keen to learn as much as possible.

Share this post


Link to post
Share on other sites

To solve this I think you are going to have to do it in at least two steps.

 

One is to offer to pay for one kiln load that you would fire according to your preferences.

If the items blow up or disintegrate with you doing the firings ... then go to your clay to look for answers.

 

Trying to change both at once is just going to confuse things and string out the whole process.

Hi Chris - I do want to make this offer with the next load.  It's a small kiln so not a big deal to fill up.  Gives an excuse for lots more testing too :)

Share this post


Link to post
Share on other sites

old kilns can be good kilns.  i don't ever remember seeing a thermocouple until i got my L&L in 2003 or so.  i have several old kilns and know there is no reason a thermocouple would have been needed.  old kilns are strictly mechanical, the cone in the sitter melts enough to lower the rod, the back of the rod makes the weight fall, the weight hits the on button and turns it off.

 

when these things were made back in the day, we had radios with two buttons or dials, on/off and station choice.  simpler times.

Share this post


Link to post
Share on other sites

Even if the 

 

 

The easiest solution would be to ask your friend to email you the firing schedule, then post it here. That way we could know what was going on and help you solve the issue. 

 

I will get the firing schedule.  My pride has now calmed a bit and it seems from this thread that it's also about drying my pots further.  I would very much appreciate some help with the firing schedule.  She has a VERY old kiln - nothing computerized.  I've been given a Kiln that may be even older and doesn't even have a thermocoupler.  I'm having the people out in the week to try and see if it's worth fixing.

 

Thank you all again very much.  I'm keen to learn as much as possible.

 

 

Even if the kiln isn't digital, she should still have some idea what the rates that she is firing are. Like Chris said, you need to isolate the issue to figure out the problem. Always just change one thing at a time. If you can get the schedule we can easily tell that if its going to quick in the beginning its going to explode pots. Even pots that feel completely dry still need a slow starting rate to be sure, because even the smallest measurement of water in a pot can still lead to a pretty violent explosion if taken up to fast. <-- learned from experience... 

 

The safest bet is if the pots feel completely dry to heat the kiln in the bisque firing along something like 90F an hour to 180F with a small hold(15-30 minutes). Increase the hold the more unsure you are about the dryness of the pots. After that you can go as fast as you need depending on the burnout for your clay. When I bisque clean clays, I go pretty fast after I am confident the water is gone. 

Share this post


Link to post
Share on other sites

old kilns can be good kilns.  i don't ever remember seeing a thermocouple until i got my L&L in 2003 or so.  i have several old kilns and know there is no reason a thermocouple would have been needed.old kilns are strictly mechanical, the cone in the sitter melts enough to lower the rod, the back of the rod makes the weight fall, the weight hits the on button and turns it off.

 

these things were back in the day we had radios with two buttons or dials, on/off and station choice.  simpler times.

Man, you are OLD!Back in art school, we had an electric kiln that didn't even have dials. Each element was turned by a separate switch, like a light switch. My prof said that this kiln design would never fail or breakdown as it was a simple design. Twenty years later, I saw that kiln, for sale, used at my clay supplier. Would have bought it, but I didn't need another kiln. All it had were the switches and a mechanical kiln sitter.

TJR.

Share this post


Link to post
Share on other sites

 

Chris, that sounds a lot like the Scientific Method, and there's no place for that kind of thing here...

Don't we just go by the seat of our pants? Chris is being too methodical. Logical.

TJR.

 

Now I know why my jeans need patching in that area!!

Thing is seat of pants become more reliable flying after a number of decades.

Grype you seem to be spending a lot of time on that couch drinking whatever and philosophising .... and you're absolutely right! Power of suggestion off to have  a tea before I go pot.

Share this post


Link to post
Share on other sites
:D 

old kilns can be good kilns.  i don't ever remember seeing a thermocouple until i got my L&L in 2003 or so.  i have several old kilns and know there is no reason a thermocouple would have been needed.  old kilns are strictly mechanical, the cone in the sitter melts enough to lower the rod, the back of the rod makes the weight fall, the weight hits the on button and turns it off.

 

when these things were made back in the day, we had radios with two buttons or dials, on/off and station choice.  simpler times.

OLD LAdy, some of us had to fire with wood!!

Share this post


Link to post
Share on other sites

Okay - I've tried the high tech so here's the low tech - just going to copy the damn firing schedule here.   I think I've realized what she did and while ask asap.  I think she totally skips the warm up on setting 1.

 

 

Bisque Firing to 980C

 

1) Keep door closed throughout the firing 

2)Leave the bung out of the door and chimney.  Set energy regulator on no. 1 and leave overnight 

3)Set energy reg. to "2" for 2 hrs

   Set energy reg. to "3" for 2 hrs

   Set Energy reg. to "4" for 1 hr

   Set Energy reg  to "5" for 1 hr

   Set Energy reg  to "6"   put bung in door, leave chimney plug open.  Leave until desired temp is reached or cones bent.

4) The kiln can then be switched off.  Make sure that the main regulator is switched off.

5) The bung in the door should not be removed above 400degrees Celius (approx 12hrs)

 

If the more scientific and knowledgeable of you wonderful folks could PLEASE explain to me what the Energy regulator 1-6 do I'd LOVE to know because it would help me be much more methodical when I try the raw firing at a later date.  I want to follow Stephen Hills firing schedule if possible.  I was doing my best before and it did work but it wasn't very scientific.

Share this post


Link to post
Share on other sites

I've never heard of an "Energy regulator" on a kiln.  I'm guessing that's just the dials, that control the elements?  Some of the dials are numbered, some just have a low, medium and high.

 

Also, with step one, and two, most people leave the kiln lid cracked, or even completely open, through this.  It allows the moisture to escape better.  Leaving the bung out will do this to some extent.  It just depends on how damp the load is overall.  

 

I hope this helps.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this  

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.