Jump to content


Photo
- - - - -

Kiln Firing Time/time To Replace Elements?


  • Please log in to reply
16 replies to this topic

#1 DBPottery

DBPottery

    Newbie

  • Members
  • Pip
  • 9 posts
  • LocationTampa, FL

Posted 18 January 2014 - 04:29 PM

Hello everyone! I can across this forum through some Google searching and it had some good information so I thought I would join.

 

I throw stoneware and fire to cone 5/6 fire for my glazes. I started with clay at age 8 and starting throwing at age 12. Now being 22 I've been at it for a while (whenever free time allows).

 

Anyways, to set the background to the question, I have an old manual Jen Kens kiln I got used 12 years ago. We were not sure how old it was when we bought it but after having the local kiln repair guy replace a bad switch 3 months ago he mentioned the kiln was at least 30 years old and in great condition because it didn't appear used much for its age. I talked with him about knowing when it was time to replace the elements. I've never replaced them since I owned the kiln and I have no idea when the previous owner replaced them because he had past away and it was his family selling the kiln. I have fired this kiln at least 125 (probably more) times since I have owned it (first 3 years cone 06-04, last 9 years 04/05 bisque and cone 5 for glaze).

 

This is my first kiln so I have no other kiln to compare firing times to, to tell if the firing times were too long to begin with. So I wanted to get an idea of what others firing times are for certain cones. I know it depends on many factors but I wanted to get a basis. 

 

My kiln (approximately- my kiln usually varies .5 hours to and hour depending on load size):

Cone 04/05 7.5-9 hours

Cone 5 14-16 hours (on average- one load took 12 hours and had one load take up to 18 hours)

 

Recently I have been monitoring this kiln more with the pyrometer. The kiln gets to 2000 degrees in decent time (in my opinion), but it seems the last 150 degrees are taking longer than it should be to get to a cone 5. The last 150 degrees it is at least 5-6 hours of the firing.

 

Thank you in advance,

 

Daniel 

 

 



#2 neilestrick

neilestrick

    Neil Estrick

  • Members
  • PipPipPip
  • 2,497 posts
  • LocationGrayslake, IL

Posted 18 January 2014 - 04:37 PM

If it's taking that long, and has that many firings on it, there's good chance it needs elements. But first, make sure it's rated to go to cone 5/6. Check the serial plate. If not, then there's the problem, but it still probably needs elements.

 

Next time have your repair guy check the elements for wear. He can do it by checking the resistance of the elements with an Ohm meter. Once they're 10% off from original, they need replacing.


Neil Estrick
Kiln Repair Tech
L&L Distributor
Owner, Neil Estrick Gallery, LLC
www.neilestrickgallery.com

neil@neilestrickgallery.com

#3 DBPottery

DBPottery

    Newbie

  • Members
  • Pip
  • 9 posts
  • LocationTampa, FL

Posted 18 January 2014 - 04:46 PM

Yes, it is rated to 2300 degrees so it's good for cone 5/6. 



#4 neilestrick

neilestrick

    Neil Estrick

  • Members
  • PipPipPip
  • 2,497 posts
  • LocationGrayslake, IL

Posted 20 January 2014 - 05:31 PM

So something is definitely wrong. Could be elements, could be a fried wire or connection, could be a bad switch, could be.........

 

You should be able to get to cone 6 in under 10 hours, so something is definitely wrong. Assuming all else is good, then the elements are worn. Do they look pretty crispy- bunching up and laying over?


Neil Estrick
Kiln Repair Tech
L&L Distributor
Owner, Neil Estrick Gallery, LLC
www.neilestrickgallery.com

neil@neilestrickgallery.com

#5 DBPottery

DBPottery

    Newbie

  • Members
  • Pip
  • 9 posts
  • LocationTampa, FL

Posted 20 January 2014 - 10:13 PM

Thanks for the replies so far. I'm not sure how to answer your question because I have nothing to compare the elements to. I have attached a picture if that helps. 

 

Daniel 

Attached Files



#6 neilestrick

neilestrick

    Neil Estrick

  • Members
  • PipPipPip
  • 2,497 posts
  • LocationGrayslake, IL

Posted 21 January 2014 - 09:11 AM

They don't look bad at all. But you'll have to check the elements resistance to be sure. Have you confirmed that all the elements glow? Could be that one is fried, or another switch burned out.


Neil Estrick
Kiln Repair Tech
L&L Distributor
Owner, Neil Estrick Gallery, LLC
www.neilestrickgallery.com

neil@neilestrickgallery.com

#7 DBPottery

DBPottery

    Newbie

  • Members
  • Pip
  • 9 posts
  • LocationTampa, FL

Posted 21 January 2014 - 08:07 PM

I just checked again to be sure, all the elements do glow. I'm going to take it over to the kiln repair shop soon and see what he thinks. 

 

Thanks again for the help!

 

Daniel 



#8 DBPottery

DBPottery

    Newbie

  • Members
  • Pip
  • 9 posts
  • LocationTampa, FL

Posted 09 March 2014 - 10:44 AM

Thanks again for the help!

 

I just got the kiln back from getting the elements replaced a few weeks ago and that was most certainly the issue. Using my normal firing schedule I had been using it got to cone 5 in 4 hrs 35 min on the first shot. That firing schedule is pretty aggressive so I slowed it down by giving low and medium a few more hours of time before going to high and that got me to cone 5 in just short of 10 hours on the second shot. 

 

I just wish I could figure out a good way to cool this manual kiln down a bit slower. I think that the fast cool down is causing the glazes to have a few more bubbles now. I'm pretty sure that the bubbles had plenty of time to smooth out before the elements got changed because it took sooooooo long to get to a cone 5/6. Now this is where a digital firing kiln could really come in to help me out. 

 

At least now I can do some trial and error more easily because the kiln isn't sweating to get up to cone 5/6. 

 

Daniel



#9 Benzine

Benzine

    Socratic Potter

  • Members
  • PipPipPip
  • 1,559 posts
  • LocationThe Hawkeye State

Posted 09 March 2014 - 01:11 PM

Daniel,

In order to control the cool down, you could just keep the controls going longer. If you are using a kiln sitter, just use a higher cone, so it doesn't shut off. A little soak time at the end of your firing could be all it takes, to get rid of the bubbles. The downside is that you will have to closely monitor the kiln at that point, so you can shut it down.
"Anything worth believing, is worth questioning"

#10 Denice

Denice

    Advanced Member

  • Members
  • PipPipPip
  • 658 posts
  • LocationWichita, Kansas

Posted 09 March 2014 - 01:30 PM

I know it means spending more money but you could get a dual digital pyrometer set ( single read-out with two probes)  to gauge your soak at the top and bottom of your kiln.  I bought a single at first but still wanted better control so I got the second probe to add to my pryrometer,  I purchased the Skutt dual pyrometer.     Denice



#11 Babs

Babs

    Advanced Member

  • Members
  • PipPipPip
  • 893 posts

Posted 09 March 2014 - 07:32 PM

I have a manual and you can prop the kiln sitter on after it has released and manually ease off hte input., or as Benzine wrote kiln sitter a cone higher then you have to watch. when witness cone has touched its toes, start to manulally fire down.

Why do you want to fire down?

There are specific temps that you can free fall.... Neil would be the man for that.

The slow cool would not alleviate the bubbles, a soak may, or a slowing down of the last part of the firing cycle.

The bubbles may be a prob. in your bisque firing as John B has explained a number of times, may be in the FAQs on these forums.

A pic of those bubbles will help the gurus to diagnose.



#12 DBPottery

DBPottery

    Newbie

  • Members
  • Pip
  • 9 posts
  • LocationTampa, FL

Posted 10 March 2014 - 08:43 PM

Thanks for the replies. In the end, I'm just trying to get rid of the bubbles. I'm not saying that my bisque firing doesn't have anything to do with it, but I never got bubbles with these glazes before prior to the element change. 

 

Denice, I have that Skutt Pyrometer too! I love it. I have always thought of getting a second thermocouple for it.

 

I have attached some pics of the bubbles. I tried the best I could to get a picture of them but some things are just hard to see in pics.

 

Daniel 

 

 

Attached Files



#13 bciskepottery

bciskepottery

    Advanced Member

  • Members
  • PipPipPip
  • 1,408 posts
  • LocationNorthern Virginia

Posted 10 March 2014 - 09:35 PM

Your bubbles have sharp edges on them. That indicates possible outgassing from the clay body while the glazes are cooling or a rapid drop in temperature that freezes the glaze while it is still boiling. Looking back, your bisque firing time seems a bit short (7 to 9 hours); as a result, all of the impurities in the clay body are not burning out. You want your last one or two hours of bisque to be a slow climb to allow carbon and other impurities to burn out -- and it looks like you are using a speckled stoneware with iron and/or manganese flecks. Also, consider adding a short hold at top temperature for bisque. Same for glazing, you want the last couple hundred degrees to be a slow climb to allow glazes to melt thoroughly and completely. And, consider adding a short hold at the top to allow even melting.

Consider picking up a copy of Hamer/Hamer's The Potter's Dictionary of Materials and Techniques and/or Harry Frazier's Ceramic Faults and their Remedies. Both have pictures of most conceivable problem you'll run into, along with good suggestions for overcoming the problems. Great diagnostic books that all potters should own.

#14 Benzine

Benzine

    Socratic Potter

  • Members
  • PipPipPip
  • 1,559 posts
  • LocationThe Hawkeye State

Posted 10 March 2014 - 09:35 PM

Nice glaze!

 

Those are what I was thinking they were, when you first described them.  I've heard debris on the bisque, can lead to that, which is one reason I wash my bisqueware well before glazing.  However, I still think that, the glaze just isn't having enough time to fully smooth out.  It bubbles a bit, when it melts, and if it doesn't reach maturity, and/ or cools too quickly, you get those.  I've had that happen in both an electric kiln, and a gas fired Raku kiln.  In the electric kiln, adding a soak at the end helped, and for the Raku kiln, I had to alter the ports, so the kiln reached temperature more efficiently. 


"Anything worth believing, is worth questioning"

#15 Babs

Babs

    Advanced Member

  • Members
  • PipPipPip
  • 893 posts

Posted 10 March 2014 - 11:18 PM

Agree with Benzine, you may have to fill the holes with a little glaze, fire slightly higher and soak as suggested.Slowing down to the end would also help

#16 DBPottery

DBPottery

    Newbie

  • Members
  • Pip
  • 9 posts
  • LocationTampa, FL

Posted 23 March 2014 - 01:59 PM

Thanks for the replies. 

 

I am making some progress on the firings. My last firing came out pretty good. Basically once the kiln got to 2000 degrees I pretty much decided to baby sit it. From 2000 till finish I would put all switches on high for 5-10 min then switch it it back down to top on med and bottom on high for 20-30 minutes. Yes, it's a lot of work, but that's really the only way for me to slow down the last part of the firing. Then, once the cone tripped the kiln sitter I turned the kiln back on for 20 minutes on med/high. Needless to say I'm counting the days until I can get a digital kiln to do this all for me. If I wasn't moving in the next year I would probably just have gotten one by now. 

 

My method allowed me to eliminate all the bubbles on the light blue glaze I posted a picture of above. 

 

Thanks for the complements on the glazes. Yes, that clay is a stoneware with manganese flecks. It's Highwater's Speckled Brownstone. Something I just found though is that many of my glaze imperfections seem to be with clays that have the manganese flecks. I started looking around at all my work that is stoneware with no manganese flecks and the glazes are much smoother. The manganese flecks seem to be causing many pin holes where the speck is and with matt glazes they have pin holes in general. Do the manganese flecks outgas a lot more or something? 

 

‚ÄčI do have a question about the bisque firings. I have looked more into theories behind how to properly bisque fire since that was suggested that it may be part of the problem and got some good insight to test on my next round of bisque firing. I was wondering how tight everyone packs their kiln for a bisque firing? From what I have read on this forum and other places I think I may be packing my kiln too tight. For example I would stack 3-5 plates on top of each other and put 1-2 smaller bowls inside a larger bowl. Should I really be making sure all pieces are placed in the kiln separately? 

 

Thanks again,

 

Daniel 



#17 bciskepottery

bciskepottery

    Advanced Member

  • Members
  • PipPipPip
  • 1,408 posts
  • LocationNorthern Virginia

Posted 23 March 2014 - 05:42 PM

Regarding your bisque stacking, bowls inside another and 3 to 5 plates does not seem too much. More important is the time allowed for burning out carbon and other impurities that could present problems during glaze firing. I try to pack my bisque loads fairly tight whenever possible, but not crammed.




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users