Firing my new kiln: bisque temperature?

[JeanWW]

I'm still trying to get to grips with my new electric kiln.  I've been reading up about bisque firing and trying to decide what to program into the controller.  I know a lot of you use cones, but I basically want to put some programs into the controller and this means deciding on ramps and temperatures.  (I'm in the UK.)  I'm getting quite a range of advice and would like your ideas please!  

What is the top temperature you use for bisque?  And what ramps do you use?  How do you decide?  I'm mostly making handmade stoneware with additions on the surface, such as seeds, that burn away in the firing.  Some of my larger pots have varying thicknesses.  Later they are very lightly glazed, or sometimes not glazed at all.  In the past I have had pots fired when attending classes and they have just gone into the kiln with all the others, so I had no idea that there were so many decisions to be made.  I thought there was such a thing as a standard bisque firing schedule and actually I thought the kiln + controller came with some standard programmes in it already, but it seems the manufacturers have changed this.  They have suggested as a typical bisque firing:

Ramp 1:   80C (176F) per hour  up to 600C (1112F)

Ramp 2: 120C (280F) per hour up to 1020-1040C (1868-1904F)

However, elsewhere I have seen Ramp 1 at 60C (140F) or 100C (212F) per hour,  and Ramp 2 at 200C (414F) per hour or FULL.   And I think this top temperature is too high for stoneware, but what should it be? Temperatures suggested have ranged from 870C (1598F) to 1000C (1832F).

Any advice, please?

 

  

[Babs]

To ensure that your pots are thoroughly dry  I would suggest 

Ramp 1: 25d C/ hr to 100dC

Ramp2: 100dC to 700dC

Ramp 3: 150dC to top bisque temp. I go to 1000dC for my pots C 06 , Others go to C04  1040dC. Depends on how your clay behaves in the glaze firing.  

Some people do a hold around 700dC to allow the chemically bound water to escape. Others Don't.

Depending on thickness of the uneven constructions this should work.

You have had your pots fired by a studio with success? Ask for their firing schedule.

Can dry out pots really well? Skip ramp 1.

Used to be bisque were C08  but that has changed with fashion. Pinholing in glazes can be caused by gas releasing from clay so folk bisque to cone 04 to remove this effect and adjust their glazes accordingly.

Take notes of what you did and outcome and adjust accordingly.

Pots blowing up usually due to moisture in the structure.

 

[JeanWW]

Thank you very much, Babs.  That's really helpful.  

[Chilly]

Hi @JeanWW

I'm also in the UK.  Every kiln is different, even those made on the same day will vary.  You will only get to know your kiln by firing it, keeping a log and by using cones.  The digital programmer will attempt to do what you ask, but the kiln itself may not be capable of achieving a particular heat rate, or it may lose heat too quickly, or you might have more ware in this week than you did last week.

It's a bit like learning to drive a car, many lessons, but no real destination.

I will say it again, use cones.  They are the only way you will know what your kiln is up to, they tell you the amount of heat/work done.  It's a bit like you can't put a fruit cake into a cold oven and expect it to be cooked by the time the oven reaches the required temperature.  Your cake needs time and heat.  Your pots are the same.

Some people use cones every single firing, week in, week out, others only use them as a learning tool, others never do, but without experience it is like driving a car without a speedometer and hoping not to break the speed limit.  There are potters on this forum in all the above camps, but most have many years experience.

 

I'm waiting for my kiln to cool at this very moment, having fired it overnight.  I did not use cones, as I was firing a small amount of porcelain that will be wood-kiln fired this weekend, so I'm not too fussed about actual final temperature, and I know my kiln.

The programme that I used is:  20C per hour to 100C, hold 30 minutes.  150C per hour to 1,000C, hold 30 minutes.  The reason for the very low. slow start is that the pots were not fully dry, but were quite thin.  The first hold gives time for the temperature to stabilise in all parts of the kiln and for water to boil off.  The same, but to a lesser degree with the second hold.  I could probably have not bothered with the second hold, but it was there from a previous firing, so I thought "why not".

 

Sounds like you are not attending classes now, or I'd advise you to talk to the techs who fired there.  In the long term clay and firing costs are low compared to your time, so load up your kiln, set it going and see what happens.

Good Luck

[Babs]

Depending o  the clay  there are a couple of interesting molecular structural changes in the clay last one occurring about 580 C ish. From memory. 570 rings a louder bell. The size of certain molecule in clay body expands quite significantly.

Thus my slower rise to 600d C  

Hope clay glaze nerd pops in here.

But if your clay handles the quick rise.....

[JeanWW]

Hi Chilly & Babs

Thanks for all the advice. 

Chilly - I've read up on using cones to measure heatwork rather than just relying on temperature and it definitely seems  a good idea.  I even asked the manufacturer if the kiln could be used without the controller.  The answer was No.  And the controller has no set programmes.  So I have to put some numbers in. 

As I make big pots which take a lot of time and effort to build, I don't want to lose them!  Perhaps I will go for a slow ramp to be on the safe side.  (Although the other side of the argument is that I want to be as economical as possible.)

Distilling all the advice:  

1.  Very slow to dry out pots (if necessary) - 20-25C/hr to 100C

2.  Slow to 600C - no more than 100C/hr (+ possibly hold)

3.  150C/hr to 1000C (+ possibly hold)

Presumably I leave the bungs out for ramps 1 & 2?   And also for cooling?  (I have one in the lid and two in the sides)

I have not yet finished building the pots for the first firing, and then they will have to dry, and at some point a decision will have to be made!

By the way, out of interest, if you teach a class, do you teach your students how to fire a kiln?

 

[Benzine]

2 hours ago, JeanWW said:

 I even asked the manufacturer if the kiln could be used without the controller.  The answer was No.  And the controller has no set programmes.  So I have to put some numbers in. 

As I make big pots which take a lot of time and effort to build, I don't want to lose them!  Perhaps I will go for a slow ramp to be on the safe side.  (Although the other side of the argument is that I want to be as economical as possible.)

 

By the way, out of interest, if you teach a class, do you teach your students how to fire a kiln?

 

I've dealt with a couple different types of kiln controllers.  Both were programmable, but one had preset programs I *could* use, and the other did not.  For my bisque firings, I have always used my own program, and rarely have issues. 

It is always best to err on the side of caution with labor intensive work.  The general rule/ philosophy with ceramics and pottery,  is to not get too attached to things, because inevitably, something bad will happen to them.  It is a very difficult concept to overcome, but as you make, more and more wares, it does get easier. 

I teach high school, in the States, and I give my students and overview of the kiln, but do not teach them how to fire it.  I will have them help load on occasion. 

When I took Ceramics in college, we also were not taught how to fire, at least the beginning class. 

My first experience with firing was in one of my Art Education classes.  We had a VERY brief overview, of firing, with a kiln setter controlled kiln.  After that, I helped fire the kiln during student teaching, on one occasion.  My first teaching job, I replaced an instructor, who did a lot of ceramics.  So it was a trial by fire kind of thing, and I learned a lot about firing then, and made a lot of mistakes along the way.

[Min]

On 10/15/2018 at 3:21 AM, JeanWW said:

I'm still trying to get to grips with my new electric kiln.

If it's a brand new electric kiln that has never been fired before then the first firing should be with an empty kiln to oxidize the elements. It should have come with directions on how to do this. If not let us know and someone can post the info on a firing schedule for doing that.

[Benzine]

4 minutes ago, Min said:

If it's a brand new electric kiln that has never been fired before then the first firing should be with an empty kiln to oxidize the elements. It should have come with directions on how to do this. If not let us know and someone can post the info on a firing schedule for doing that.

I just installed new elements, and went full power until Cone 6.

[JeanWW]

Hi Min

I've done that (with help from this site).  Next step is bisque.  When I've done that, I may be back for more advice!

[Babs]

Big pots go slow and place them on,  i use fine grog, others use other stuff. This allows them to move smoothly as they contract during firing.

Bungs out till..I leave out till 600 ... then all in until kiln is cool. Don' crack it before 150 others go lower. Kiln furniture bricks etc don' like it.

Go make more pots if you are tempted.

 

[Chilly]

On 10/19/2018 at 11:49 AM, JeanWW said:

(Although the other side of the argument is that I want to be as economical as possible.)

 

By the way, out of interest, if you teach a class, do you teach your students how to fire a kiln?

 

Your time and effort are more expensive than the cost to fire your kiln.  Do you know how much it does cost? 

To work it out you need the kwh cost from your supplier and the rating of your kiln.  If you fire it at full blast for say, 8 hours, the total cost would be 8 x kwh cost.  As you will not be firing at full blast for that long, cost will be lower.  My kiln has a button that will tell me kw useage after it's fired.  My last bisque (very slow) used  (I think) 14kw.  At 8.19p per kwh it cost maximum of £1.20 to fire.  Considering the hours of work put into making "stuff", the firing cost is minimal.

 

I assist the tutor, and am the person that fires the kiln at the centre.  I will teach anyone who shows an interest, but not necessarily include it as part of the class.

 

Remember the driving lessons.  Lots of time, energy and cost,  you didn't actually go anywhere, but you learned lots.

[JeanWW]

Oh dear, I hope it doesn't take as long as I took learning to drive!

[LeeU]

Using cones is invaluable. I put a pac of 3 on each level in the kiln (bottom, middle, top). Different levels may run cooler or hotter than others, which is good to know! I don't know if you are in the U.S. or overseas, but my almost 5 cubic ft. electric kiln only costs about $8  per firing, and electricity is expensive in my area.