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SydneyGee

My Favorite Clay Types + Glazes: Whats The Recipe For Perfect Bisque And High Fire Glazes?

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After all the fun stuff is gathered (kiln, wheel, tools, clay, glazes) and you are ready to throw your work into the fiery pit, what temperature should that pit be and how long should you bisque it? I have my favorite clays and glazes (I am using my professors kiln and wheel for now until I get my kiln at home figured out) but I have yet to get a good answer on the correct temperatures and times my bisque firings should be in the kiln. I have mostly been observing and creating the works with glazes while others load and monitor the kiln/firing process (plus they are massive front load kilns over 6' tall and 6' wide).

 

Here is the scenerio:

 

I am using Amaco No. 58 (a red clay). It is a cone 5 clay, but what temperature/cone and how long do I bisque it? I want to put a Cone 5-6 Amaco Shino glaze on it. I load the kiln with the glazed pottery and leave it in there at the setting of cone 5 for how long? I understand it sort of varies depending on the quickness and efficiency of the kiln, but what is the general rule?

 

I am using Amaco No. 11 (a off white clay). It is a cone 5 clay. Same as above, what cone and how long do I bisque it? I want to put on a Cone 5-6 Amaco PC33 Iron Lustre glaze. Once the pots are glazed how long will it take in the kiln?

 

I am just looking for general estimates and I chose simple clays with same-brand glazes to reduce the possibility of bubbling/bloating/other problems. I will be keeping a log and most likely be testing my kiln for quite a while before I delve into putting my better work in it. Any simple formulas would greatly be appreciated!

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sydney, it appears that you are thinking in terms of cooking, bake the cake for 35 minutes and turn off the oven.

 

that is not how firing goes.  what kind of kiln are you firing, is it electric,  does it have a kiln sitter into which you put a cone?  do you use a kiln with an electronic controller?

 

the time is not the important thing, the amount of heat and time combined is what is important.  and that cannot be answered here.  if you have 2 pieces in an otherwise empty kiln there will be a different amount of time than if you have loaded the kiln from top to bottom.  

 

you might benefit from some good books on firing.  it is a part of your education that you cannot neglect.

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A common bisque temperature is either cone 05 or 04; some fire fast schedules, others fire slow schedules.  Ask a dozen potters, you may end up with 13 answers.  Some potters prefer a hard bisque item as it absorbs less glaze; others prefer a soft bisque.  Most studios bisque higher as the harder bisques helps compensate for beginner glazers who tend to apply glazes too thick, resulting in runs on the kiln shelf. 

 

Not knowing your kiln type (assuming electric) -- manual or digital controller -- makes it hard to suggest a temperature schedule.  Find the operator manual from the kiln manufacturer (most post them on-line at their websites) and see what they recommend.  Most start with a low temperature to get any dampness out of the greenware, then progressively increase heat until you hit your target temperature.

 

As you are using both a red and white stoneware clay, I'd recommend a slow schedule to at least cone 05 to allow the organics often found in red/brown clays to burn out.  Once you hit top temperature, I'd consider holding the temperature for 10 minutes to help burn out impurities, then allow the kiln to cool.

 

For your commercial glazes, follow the instructions.  And then adjust as needed.  Those glazes look good at cone 5, fine at cone 6 (mostly), but may start to be problematic above that temperature.

 

I have an L&L kiln with digital controller.  My slow bisque schedule is about 9 hours for a full load (~7 cu.ft.); I also glaze fire slow and it takes about 8 hours.  I've just changed elements, so they are new and fire faster; my old elements had a bisque of about 12 hours and glaze of about 10 hours.  I use the slow bisque and glaze programs programmed by the manufacturer with the addition of a 10 minute hold at the end for both bisque and glaze (I use multiple types of clay -- including some black --  that need to burn out the nasty things). 

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What they all said, everything thing is relative. Type of Kiln, size of kiln, controller on kiln, exhaust fan on kiln, thickness of pieces, types of pieces, how heavy the load is, how sure are you the load is dry, etc.

 

Look up the manufacturers website for the kiln you are using and download their manual. Most manuals have a firing schedule or 2 in them as a starting point.

 

I would suggest a slow bisque to begin until you are sure of water your pieces can handle anything else. I have an electric digital controlled kiln with a downdraft vent. I fire to cone 04 for bisque firing and my schedule takes about 13 hours to complete with a 10 minute hold at the end to help the heat even out in the kiln and get the heat work where I need it to be and a properly bent cone achieved. Oh! To start, as you learn ALWAYS use cones, on each shelf until you learn the cool and hot spots in the kiln.

 

Glaze firing, I use a slow glaze to cone 6 with a CNOS offset of 15 and with a hold added at the end to get the heat work where I need it and a perfectly bent cone. My glaze schedule takes about 8 hours to complete.

 

You can see with just the few answers you've gotten how different firing schedules can be that is why I suggest starting with a schedule printed in your manual.

 

Good luck!

T

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A common bisque temperature is either cone 05 or 04; some fire fast schedules, others fire slow schedules.  Ask a dozen potters, you may end up with 13 answers.  Some potters prefer a hard bisque item as it absorbs less glaze; others prefer a soft bisque.  Most studios bisque higher as the harder bisques helps compensate for beginner glazers who tend to apply glazes too thick, resulting in runs on the kiln shelf. 

 

Not knowing your kiln type (assuming electric) -- manual or digital controller -- makes it hard to suggest a temperature schedule.  Find the operator manual from the kiln manufacturer (most post them on-line at their websites) and see what they recommend.  Most start with a low temperature to get any dampness out of the greenware, then progressively increase heat until you hit your target temperature.

 

As you are using both a red and white stoneware clay, I'd recommend a slow schedule to at least cone 05 to allow the organics often found in red/brown clays to burn out.  Once you hit top temperature, I'd consider holding the temperature for 10 minutes to help burn out impurities, then allow the kiln to cool.

 

For your commercial glazes, follow the instructions.  And then adjust as needed.  Those glazes look good at cone 5, fine at cone 6 (mostly), but may start to be problematic above that temperature.

 

I have an L&L kiln with digital controller.  My slow bisque schedule is about 9 hours for a full load (~7 cu.ft.); I also glaze fire slow and it takes about 8 hours.  I've just changed elements, so they are new and fire faster; my old elements had a bisque of about 12 hours and glaze of about 10 hours.  I use the slow bisque and glaze programs programmed by the manufacturer with the addition of a 10 minute hold at the end for both bisque and glaze (I use multiple types of clay -- including some black --  that need to burn out the nasty things). 

Thank you! This is basically what I was looking for.  So it takes as long as your kiln needs to heat up? I was always under the impression the time was more important, and there was some special easy to follow recipe for the perfect firing. 

 

sydney, it appears that you are thinking in terms of cooking, bake the cake for 35 minutes and turn off the oven.

 

that is not how firing goes.  what kind of kiln are you firing, is it electric,  does it have a kiln sitter into which you put a cone?  do you use a kiln with an electronic controller?

 

the time is not the important thing, the amount of heat and time combined is what is important.  and that cannot be answered here.  if you have 2 pieces in an otherwise empty kiln there will be a different amount of time than if you have loaded the kiln from top to bottom.  

 

you might benefit from some good books on firing.  it is a part of your education that you cannot neglect.

The recipe example is spot on. As far as I knew, firing was a formula that you follow and it is across the board. In my hypothetical scenario the kiln could reach any temperature needed and the time was the only unknown factor. I see now that the firing is solely dependent on how long the kiln takes to heat up? 

 

What they all said, everything thing is relative. Type of Kiln, size of kiln, controller on kiln, exhaust fan on kiln, thickness of pieces, types of pieces, how heavy the load is, how sure are you the load is dry, etc.

 

Look up the manufacturers website for the kiln you are using and download their manual. Most manuals have a firing schedule or 2 in them as a starting point.

 

I would suggest a slow bisque to begin until you are sure of water your pieces can handle anything else. I have an electric digital controlled kiln with a downdraft vent. I fire to cone 04 for bisque firing and my schedule takes about 13 hours to complete with a 10 minute hold at the end to help the heat even out in the kiln and get the heat work where I need it to be and a properly bent cone achieved. Oh! To start, as you learn ALWAYS use cones, on each shelf until you learn the cool and hot spots in the kiln.

 

Glaze firing, I use a slow glaze to cone 6 with a CNOS offset of 15 and with a hold added at the end to get the heat work where I need it and a perfectly bent cone. My glaze schedule takes about 8 hours to complete.

 

You can see with just the few answers you've gotten how different firing schedules can be that is why I suggest starting with a schedule printed in your manual.

 

Good luck!

T

Thank you for the response! You can have the kiln lid cracked open to keep an eye on the pieces correct? Not that you could really judge much with the heat and color of the fire. But I assume using the cones as references you can see how the baking is going. 

 

To recap: firing time is dependent on the individual kiln and how long the kiln takes to heat up. Use cones to monitor firing. Keep logs and experiment. 

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If you want to monitor the cones dropping during the firing place them where they are visible through your peep holes. Do NOT open your lid during the firing you will crack all your pieces and singe your eyebrows off at the least. When you look through the peep to check during firing be sure to wear eye protection like welders glasses. Cone 04 is 1945 degrees and cone 6 is 2223 degrees there abouts this too will vary somewhat depending on your kiln and this is VERY HOT and dangerous to mess with.

 

if you have a digital controller it will automatically shut off a the temperature programmed. The cones you can then check once it's cooled off to see if you got the heat work needed. Then you can adjust the next firing up or down, you start with the basic firing schedule in the manual and adjust from there. If you are using a manual kiln you will need to go by the manual how to place the control cones in the holder, when to adjust the manual knobs, etc. I do not have a manual kiln and have never fired one so can't help there as it is much different than with a digitally controlled kiln. What kind do you have?

 

I HIGHLY recommend getting a book on kiln firing from the library or visiting and talking with someone that fires a kiln to have them explain in more detail.

 

Also it's not just turning in the kiln and heating as fast as possible to desired temperature. You will need to hold at certain temperatures to prevent the pieces from cracking, bursting, blowing up etc. For bisque you heat up SLOWLY to get the pieces safely to the desire temperature. It's more like saying of putting a frog in a cold pan of water and slowly heating it up and it will stay there and cook to death whereas if you drop a frog in boiling water it will jump out. You want your pots to sit there and safely react to the temperature increases not shock them by going too quickly. I hope that makes sense. Again borrow a book or talk to someone you know that fires a kiln regularly. Watch them load their kiln and set the firing schedule, etc.

 

 

T

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If you want to monitor the cones dropping during the firing place them where they are visible through your peep holes. Do NOT open your lid during the firing you will crack all your pieces and singe your eyebrows off at the least. When you look through the peep to check during firing be sure to wear eye protection like welders glasses. Cone 04 is 1945 degrees and cone 6 is 2223 degrees there abouts this too will vary somewhat depending on your kiln and this is VERY HOT and dangerous to mess with.

 

if you have a digital controller it will automatically shut off a the temperature programmed. The cones you can then check once it's cooled off to see if you got the heat work needed. Then you can adjust the next firing up or down, you start with the basic firing schedule in the manual and adjust from there. If you are using a manual kiln you will need to go by the manual how to place the control cones in the holder, when to adjust the manual knobs, etc. I do not have a manual kiln and have never fired one so can't help there as it is much different than with a digitally controlled kiln. What kind do you have?

 

I HIGHLY recommend getting a book on kiln firing from the library or visiting and talking with someone that fires a kiln to have them explain in more detail.

 

Also it's not just turning in the kiln and heating as fast as possible to desired temperature. You will need to hold at certain temperatures to prevent the pieces from cracking, bursting, blowing up etc. For bisque you heat up SLOWLY to get the pieces safely to the desire temperature. It's more like saying of putting a frog in a cold pan of water and slowly heating it up and it will stay there and cook to death whereas if you drop a frog in boiling water it will jump out. You want your pots to sit there and safely react to the temperature increases not shock them by going too quickly. I hope that makes sense. Again borrow a book or talk to someone you know that fires a kiln regularly. Watch them load their kiln and set the firing schedule, etc.

 

 

T

Thank you! I am not trying to rush, nor am I implying I want to be an expert on firing overnight. I am very patient when it comes to ceramics. Coming from someone who has never fired before, but been more of a baker, I am used to clear cut recipes that give directions on both temperature and cooking time. I see now ceramics firing is not an exact science and there is a lot of trial and error!

 

I appreciate the analogy and am happy to be learning the basics of firing (I posted earlier I have only been throwing and glazing, not actually touching the kiln or learning the process of firing). So all of the firing process is new to me.

 

I do not know exactly what brand of kiln they are using at the university I am studying at where I currently do all my ceramics, but I believe it is a manual front opening gas kiln about 6'x5'x5'. At home I have a small manual electric kiln. Mine, I learned, is too cool of a kiln for what I am used to using in my ceramics class (only fires to cone 02. I like to use cone 5) so I may be swapping it in for a larger automatic electric kiln that my grandmother has.

 

I am excited to continue learning about the firing process, as now that I plan to have a kiln and wheel at home I want to experiment and learn about my tools!

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 Ask a dozen potters, you may end up with 13 answers.  

 

 

So true.

 

Agree with all the comments above.  Read everything you can get your hands on, order every pottery book from your local library.  They will all describe firing in different ways, one book will jar your brain, one won't make any sense, one will make perfect sense.  Try, Try, Try again.

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learn about your kiln by finding the plate somewhere on the outside that has all kinds of numbers and things.  somewhere there is a name that means the manufacturer of that particular kiln.  once you copy all that stuff, you can search out real info on YOUR kiln, not just general info on just anything.

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