Firing times

[Alina Albu]

Hello folks

 

I am interested in reducing the length of glaze firing for my pots. I was told, or rather, I always assumed, that you need to fire slowly to about 600ºC, then get up to temperature asap. I fire at 1255ºC, electric. (sorry not familiar with cone systems).

I have come across pottery bloggers who claim the need to fire slowly is a myth. After all, the industry fires tiles in 45 minutes from crude. And once, I had some pieces of porcelain fired by a kiln technician who set up the program to finish in 6 hours! and it worked.

I use an electric kiln and don't want to damage it by doing crazy firings.

Can I really do a firing cycle for porcelain in 6 hours? Pieces previously bisqued.

Any suggestions, much appreciated,

 

Alina

[Marcia Selsor]

I think you could do a firing that fast as long as pieces were dry from glazing.

Marcia

 

 

 

[Frederik-W]

I would like to know more myself from other people's experience.

I can offer the following advice:

 

There are two critical temperatures involving rapid expansion/contraction (Quartz inversion)

at 573â°C and 220â°C. Care should be taken going through these temperatures.

 

The temperature climb up to and around boiling point 100â°C need to be slower for greenware because if steam develops it can crack/explode

 

The more grog (particles) in the clay the more resistant it will be to thermal shock. Raku clays are especially good. (Some African people use open wood firing which provide rapid heating with temperature fluctuation, but they use a lot of grog in their clay).

 

Ware which have varying thickness need slower heating.

Thick pieces need slower heating. Thin pieces can be fired very rapidly.

 

The dryer the better.

[High Bridge Pottery]

When I fire I do 1 hour to 300 degrees centigrade then just go as fast as possible up to 1240 with 30 min hold. Could probably just put it on full from the beginning. Never had any problems.

 

I also know nothing about the subject Just have the 300 because of the way the programer works and random logic.

[OffCenter]

Hello folks

 

I am interested in reducing the length of glaze firing for my pots. I was told, or rather, I always assumed, that you need to fire slowly to about 600ºC, then get up to temperature asap. I fire at 1255ºC, electric. (sorry not familiar with cone systems).

 

I have come across pottery bloggers who claim the need to fire slowly is a myth. After all, the industry fires tiles in 45 minutes from crude. And once, I had some pieces of porcelain fired by a kiln technician who set up the program to finish in 6 hours! and it worked.

 

I use an electric kiln and don't want to damage it by doing crazy firings.

 

Can I really do a firing cycle for porcelain in 6 hours? Pieces previously bisqued.

 

Any suggestions, much appreciated,

 

Alina

 

 

I use lots of different clay bodies (including porcelain) and when doing a regular cone 6 elect glaze firing simply load the kiln, shut the lid, shut all the peeps and turn all the switches to high. I don't know why anyone would do it any other way unless they are too lazy to test or just like wasting time and electricity.

 

Jim

[Pres]

Hello folks

 

I am interested in reducing the length of glaze firing for my pots. I was told, or rather, I always assumed, that you need to fire slowly to about 600ºC, then get up to temperature asap. I fire at 1255ºC, electric. (sorry not familiar with cone systems).

 

I have come across pottery bloggers who claim the need to fire slowly is a myth. After all, the industry fires tiles in 45 minutes from crude. And once, I had some pieces of porcelain fired by a kiln technician who set up the program to finish in 6 hours! and it worked.

 

I use an electric kiln and don't want to damage it by doing crazy firings.

 

Can I really do a firing cycle for porcelain in 6 hours? Pieces previously bisqued.

 

Any suggestions, much appreciated,

 

Alina

 

 

I use lots of different clay bodies (including porcelain) and when doing a regular cone 6 elect glaze firing simply load the kiln, shut the lid, shut all the peeps and turn all the switches to high. I don't know why anyone would do it any other way unless they are too lazy to test or just like wasting time and electricity.

 

Jim

 

 

I pretty much do the same, but when ^5 starts down I turn back the kiln on the top switch and the middle more at the top. This gives me a better soak, and eliminates the little bit of pinholing I get on a straight up firing. I fire without a setter and hit about ^6 1/4.

[OffCenter]

Hello folks

 

I am interested in reducing the length of glaze firing for my pots. I was told, or rather, I always assumed, that you need to fire slowly to about 600ºC, then get up to temperature asap. I fire at 1255ºC, electric. (sorry not familiar with cone systems).

 

I have come across pottery bloggers who claim the need to fire slowly is a myth. After all, the industry fires tiles in 45 minutes from crude. And once, I had some pieces of porcelain fired by a kiln technician who set up the program to finish in 6 hours! and it worked.

 

I use an electric kiln and don't want to damage it by doing crazy firings.

 

Can I really do a firing cycle for porcelain in 6 hours? Pieces previously bisqued.

 

Any suggestions, much appreciated,

 

Alina

 

 

I use lots of different clay bodies (including porcelain) and when doing a regular cone 6 elect glaze firing simply load the kiln, shut the lid, shut all the peeps and turn all the switches to high. I don't know why anyone would do it any other way unless they are too lazy to test or just like wasting time and electricity.

 

Jim

 

 

I pretty much do the same, but when ^5 starts down I turn back the kiln on the top switch and the middle more at the top. This gives me a better soak, and eliminates the little bit of pinholing I get on a straight up firing. I fire without a setter and hit about ^6 1/4.

 

 

Yes, the time to slow down is as you get within a hundred degrees or so of the max temp and then during the cool down.

 

Jim

[Alina Albu]

This is great, thanks everybody! I guess I'll go for it.

 

Marcia, I will only have a few hours to let the glaze dry. Hope that will be enough.

[Kohaku]

 

Yes, the time to slow down is as you get within a hundred degrees or so of the max temp and then during the cool down.

 

Jim

 

 

This is key- depending on what type of an effect you want from your glaze. A glaze that yields a complex, matte or crystalline surface with a slow cool-down can be translucent or even transparent if the kiln is just switched off at its peak.

 

Either may be fine... but be aware of what you want.

[Isculpt]

REALLY??? Apparently I've been wasting time and electricity! I have an old kiln with no fancy computerization, so will someone please tell me exactly what kind of firing speed is safe for 1/4"-1/2" thick earthenware or raku sculpture that has been bisqued, and is being fired with only underglazes or copper carbonate? In other words, I don't have to take into consideration glaze properties. I'm now embarrassed to admit that I spent 7 hours getting previously bisqued work up to cone 04 this week for the underglaze firing! As for the "risky" temperatures, how do you "baby" your work through those? And how fast can the cooling-down process can be without risking injury to the (in my case) sculptures? Boy, this is good news if I'm hearing what I think I'm hearing!

Jayne

[Mark C.]

You can fire as fast as your furniture can take really. The thing that folks have eluded to is that many glazes look better with some time near high points to mature. That is the time they are very near end point in a cone or temperature setting. Most glazes will look better if allowed to have a slower time around maturing temperature-that is slow down near the end so they can mature slowly. This way the crystals can mature and the glaze matrix will look better. The cool down also needs to be slower so the glaze can cool slowly from the top end. This will make your glazes look better..

If you want to really find out how this works you can try what I did in 1972 fired my small gas kiln to cone 10 then unbrick the door as soon as it turns off. This reveals all glaze /body flaws such as shivering and dunting and can lead to kiln shelve loss. You only need to do this once to learn the down side to quick cooling.

Since then I was nicknamed the Cooler King until Steve MaQueen got the name in the great Escape.

I like a two day cool now unless its a time squeeze.

Its good to test the limits in ceramics to know what they truly are as many limits taught in schools are not really where you may think.

Mark

[Alina Albu]

You can fire as fast as your furniture can take really. The thing that folks have eluded to is that many glazes look better with some time near high points to mature. That is the time they are very near end point in a cone or temperature setting. Most glazes will look better if allowed to have a slower time around maturing temperature-that is slow down near the end so they can mature slowly. This way the crystals can mature and the glaze matrix will look better. The cool down also needs to be slower so the glaze can cool slowly from the top end. This will make your glazes look better..

If you want to really find out how this works you can try what I did in 1972 fired my small gas kiln to cone 10 then unbrick the door as soon as it turns off. This reveals all glaze /body flaws such as shivering and dunting and can lead to kiln shelve loss. You only need to do this once to learn the down side to quick cooling.

Since then I was nicknamed the Cooler King until Steve MaQueen got the name in the great Escape.

I like a two day cool now unless its a time squeeze.

Its good to test the limits in ceramics to know what they truly are as many limits taught in schools are not really where you may think.

Mark

 

 

Hi Mark,

 

I am after glossy glazes anyway, don´t do any matte or crystalline. At least not for now. My issue was trying to get a slow cooling period down to 800ºC, and that was not possible on my kiln as it only has 4 phases, of which the first three were taken with the ramping up and soaking. I have to fire overnight and I am not always there to fiddle with the controls. So, what I am going to do from now on, I´ll try and get to top temp in one phase, soak in phase two, cool slowly to 800ºC in phase three, and that gives me another phase for cooling off to the end. Yep, that might work. Thanks

Alina

[Alina Albu]

Yes, the time to slow down is as you get within a hundred degrees or so of the max temp and then during the cool down.

 

Jim

 

 

This is key- depending on what type of an effect you want from your glaze. A glaze that yields a complex, matte or crystalline surface with a slow cool-down can be translucent or even transparent if the kiln is just switched off at its peak.

 

Either may be fine... but be aware of what you want.

 

 

Hi Kohaku,

At the moment I am after glossy glazes, but will bear that in mind when trying something different.

 

Like your signature line. And "All that glitters is not gold". (no, it´s my glossy glaze! hehe)

[Mart]

I guess it boils down to how often do you like to change the heating coils and relays in your kiln

I am new to pottery and "magic" of kiln firing but what I have read and told by people with years of experience - faster you heat up, faster you burn out the heating coils/wires. Simple physics.

So, I have kept my last 2 hours at 150 C/h rate, reaching the top temperature (usually 1243 or 1257).

There is another reason for this. I have no cones available, but I use electric kiln with a really good (configurable) controller. Most of the information available in English uses the cone system and all the "cone to celsius" charts use 150 C/h for last 2 hours for the conversion.

As mentioned by Frederik-W, there are few tempertaure points that are important. Add temperatures ranges, where carbon etc finally burns out, and you are back at the typical firing schedule.

 

To me, it's still mystery, what do they actually mean by "slowly". If you know, how to translate "slowly" to degrees per hour, please let me know too.

 

PS! Planet Earth hours please

[OffCenter]

REALLY??? Apparently I've been wasting time and electricity! I have an old kiln with no fancy computerization, so will someone please tell me exactly what kind of firing speed is safe for 1/4"-1/2" thick earthenware or raku sculpture that has been bisqued, and is being fired with only underglazes or copper carbonate? In other words, I don't have to take into consideration glaze properties. I'm now embarrassed to admit that I spent 7 hours getting previously bisqued work up to cone 04 this week for the underglaze firing! As for the "risky" temperatures, how do you "baby" your work through those? And how fast can the cooling-down process can be without risking injury to the (in my case) sculptures? Boy, this is good news if I'm hearing what I think I'm hearing!

Jayne

 

 

Jayne, when I suggested glaze firing bisqued ware up to almost top temp as fast as the kiln will go I said a "regular" firing. By that I meant just average pots in an average kiln. (I know, I know that's pretty damn vague.) Sculpture and huge pots may not be able to take the same firing that most pots can. And some kilns fire much faster than others. (I have a tiny test kiln that gets to cone 6 in less than an hour--or I did have one until it burned itself up when I forgot about it for 5 minutes.) I'm not saying that your sculpture can't be fired as fast as "regular" pottery and I don't think 1/4-1/2 inch is too thick to take it, but to be on the safe side I'd test a really thick piece (that's not your favorite) before firing sculpture full speed. A fast cool-down should be even less of a risk than a fast ramp up. Obviously, testing to see if it is safe (I bet it is.) to fire full blast then cool down full blast is worth it to you.

 

Jim

[OffCenter]

 

Its good to test the limits in ceramics to know what they truly are as many limits taught in schools are not really where you may think.

 

 

 

Amen!

[OffCenter]

 

I am after glossy glazes anyway, don´t do any matte or crystalline. At least not for now. My issue was trying to get a slow cooling period down to 800ºC, and that was not possible on my kiln as it only has 4 phases, of which the first three were taken with the ramping up and soaking. I have to fire overnight and I am not always there to fiddle with the controls. So, what I am going to do from now on, I´ll try and get to top temp in one phase, soak in phase two, cool slowly to 800ºC in phase three, and that gives me another phase for cooling off to the end. Yep, that might work. Thanks

Alina

 

 

I'd go with no ramp down for the cool. Like many things in ceramics something comes along and catches on and then is overdone. In another thread here I and a couple of other potters are going into great detail about cooling down fast from cone 6 to 1700 degrees and then slow down and have an hour hold at 1600. But that is because we're after a certain kind of iron saturate glaze. For most glazes, a fast cool down is fine. For your glossy glazes I can't imagine why you'd want to slow the cooling. As a matter of fact, most glossy glazes look better with a fast cool down. Even for some mattes a slow cool down is a waste of time. I tested lots of glazes that were supposed to have slow, complicated cool downs and found than many (not all) looked just as good or even better simply taken a cone higher. That extra heat work of taking them one cone higher did everything that the ridiculously complicated and lengthy recommended schedule did.

Electric firings with computers are today what cone 10 reduction was in the 80's, salt in the 90's, wood in 00's. And just as with those, one potter's perfect firing schedule is another potter's waste of time.

 

Jim

[Frederik-W]

I guess it boils down to how often do you like to change the heating coils and relays in your kiln

I am new to pottery and "magic" of kiln firing but what I have read and told by people with years of experience - faster you heat up, faster you burn out the heating coils/wires. Simple physics.

 

 

 

Hi Mart, you are correct about the switching relays/contactors deteriorating because they switch more often during a slow firing.

However I do not think you waste the elements more during rapid heating.

Most kilns that I know switch the elements hard on & off to control the temperature. More "off" periods for slow heating and more "on" periods for faster heating.

The elements do not go to a higher temperature during fast heating (they still get the same voltage), they just stay on longer. (less "off" periods)

However the added-up on-time will be less during a quick firing because the kiln does not waste time to loose as much heat.

So if the elements deteriorate because they are used more, then a quick firing will actually be better,

Unless there are other factors involved, and if there are I am happy to learn about it.

I think all the electricity you save with rapid firing will also help to buy new elements.

 

What may make your elements deteriorate more is if the atmosphere in the kiln has moisture or other gasses that add to corrosion/oxidation of the elements.

e.g. if you fire greenware with all bung holes covered from the start.

[Frederik-W]

... please tell me exactly what kind of firing speed is safe for 1/4"-1/2" thick earthenware or raku sculpture that has been bisqued, and is being fired with only underglazes or copper carbonate?

Jayne

 

 

Hi Jayne,

I also do earthenware sculptures, often without glaze, with raku clay or groggy clay.

I still want to experiment with how fast you can go, but I can tell you that you can go much faster that the "normal" rates of e.g. 100degrees/hr.

Raku clay is made to withstand being taken out of a raku gas kiln at peak temperature into cold atmosphere, so they can withstand a lot of thermal shock.

They are also made to withstand being fired in a raku gas kiln in a few hours, e.g. I have seen 1000 degrees Celcius in 2hrs (that is if they are bisqued beforehand).

So don't be shy to go fast.

I am much encouraged by all the good news I read here about rapid firing.

Save time, save electricity, save on greenhouse gas emmissions.

[Mart]

I guess it boils down to how often do you like to change the heating coils and relays in your kiln

I am new to pottery and "magic" of kiln firing but what I have read and told by people with years of experience - faster you heat up, faster you burn out the heating coils/wires. Simple physics.

 

 

 

Hi Mart, you are correct about the switching relays/contactors deteriorating because they switch more often during a slow firing.However I do not think you waste the elements more during rapid heating.Most kilns that I know switch the elements hard on & off to control the temperature. More "off" periods for slow heating and more "on" periods for faster heating.The elements do not go to a higher temperature during fast heating (they still get the same voltage), they just stay on longer. (less "off" periods)However the added-up on-time will be less during a quick firing because the kiln does not waste time to loose as much heat. So if the elements deteriorate because they are used more, then a quick firing will actually be better,Unless there are other factors involved, and if there are I am happy to learn about it.I think all the electricity you save with rapid firing will also help to buy new elements.What may make your elements deteriorate more is if the atmosphere in the kiln has moisture or other gasses that add to corrosion/oxidation of the elements.e.g. if you fire greenware with all bung holes covered from the start.

 

 

Thank you for your reply. I never thought about it like that

I actually thought that relays and wires (elements) burn out faster if you pump more juice trough them - going up faster.

 

I am going to try switching to 200 C/h from 150 and see what my power meter shows.