[JoyB]

Hello from England, I think I need to ask, (1) can anyone explain 'Heat work' to me please, in plain english as I am finding it hard to get my head around, and (2)how does the speed of firing effect the final temperature reached?(3) does how the kiln is packed have much effect on thisI ask because I have a new 150litre Rhode top loading electric kiln with its own controller .. no sitter.  I set the ramp 150d c up to 610d c, then 300 d c ramp to 1225d c with a 15minute soak.My Orton large pyrometic cone 9 is either flat or touching its toes depending on which shelf Slightly different temp on the control to what the cone is telling me (and I wonder what would happen if I set the controller to 1260c? which is the temp I am aiming at) One of the reasons I need this explaining is, if possible, I want to be able to put larger sculpture in the same firing as my domestic ware but I think it should be slower firing for the sculpture, but at the same time I want the glaze on my smaller ware to come out the same as it does on the faster firing.Is a slower firing going to effect the heatwork and my glazes reactions, I use two or more glazes layered on top of each other. If I cant do this then what happens If I only put one piece of sculpture in, will it get hotter quicker? what would the temp and ramp be as I guess what/how the kiln is filled must have some bearing on results?I am hoping to understand this so that I can adjust for future firings.Many thanks and sorry for such longwinded questions Joy

[neilestrick]

Cones measure heat work. Heat work is a function of temperature over time. It takes time for heat to penetrate and have an effect on the pieces in the kiln. Therefore, a faster firing will have to reach a higher temperature to get the same amount of heat work as a slower firing.

Think about cooking a pork roast. You can cook it at 350F degrees for an hour, or at 225F degrees for 4 hours. Either way you have the same amount of heat work and a cooked roast. The difference in a kiln is that we are primarily dealing with climbing temperatures rather than holding temp like in an oven. That said, holding temperature at the end of a firing has the same effect as firing hotter. A 20 minute hold is roughly equal to firing one cone higher.

As for how your glazes will respond to firings of different speeds, that all depends on your glazes. Cone 9 is cone 9 from a melting standpoint. However slower firings often give more richness to the glazes. Test, test, test.....

[JoyB]

neilestrick, on 08 August 2012 - 11:17 AM, said:

Cones measure heat work. Heat work is a function of temperature over time. It takes time for heat to penetrate and have an effect on the pieces in the kiln. Therefore, a faster firing will have to reach a higher temperature to get the same amount of heat work as a slower firing.

Think about cooking a pork roast. You can cook it at 350F degrees for an hour, or at 225F degrees for 4 hours. Either way you have the same amount of heat work and a cooked roast. The difference in a kiln is that we are primarily dealing with climbing temperatures rather than holding temp like in an oven. That said, holding temperature at the end of a firing has the same effect as firing hotter. A 20 minute hold is roughly equal to firing one cone higher.

As for how your glazes will respond to firings of different speeds, that all depends on your glazes. Cone 9 is cone 9 from a melting standpoint. However slower firings often give more richness to the glazes. Test, test, test.....

Hey, Thanks Neil, that's a neat way of explaining heatwork, very understandable.
Many thanks

Joy

[JoyB]

neilestrick, on 08 August 2012 - 11:17 AM, said:

Cones measure heat work. Heat work is a function of temperature over time. It takes time for heat to penetrate and have an effect on the pieces in the kiln. Therefore, a faster firing will have to reach a higher temperature to get the same amount of heat work as a slower firing.

Think about cooking a pork roast. You can cook it at 350F degrees for an hour, or at 225F degrees for 4 hours. Either way you have the same amount of heat work and a cooked roast. The difference in a kiln is that we are primarily dealing with climbing temperatures rather than holding temp like in an oven. That said, holding temperature at the end of a firing has the same effect as firing hotter. A 20 minute hold is roughly equal to firing one cone higher.

As for how your glazes will respond to firings of different speeds, that all depends on your glazes. Cone 9 is cone 9 from a melting standpoint. However slower firings often give more richness to the glazes. Test, test, test.....

Just looking at my post, it's lost all it's spaces and paragraphs! Not sure how that happend but it looks hard to read so sorry about that!

Joy

[yedrow]

I have been under the impression for a while that time at temp. equals something like saturation. So, if you fire a piece of pottery at 1000 c. in five hours it isn't actually the same as firing at 500 c. in ten hours. The same amount of heat work has been done, but the material being heated lags in its change on a molecular level in the sense of crystal growth/saturation. I could well be wrong and am interested in a better explanation. It wouldn't be the first time I've been bitten by a 'fond notion'.

[neilestrick]

yedrow, on 08 August 2012 - 08:34 PM, said:

I have been under the impression for a while that time at temp. equals something like saturation. So, if you fire a piece of pottery at 1000 c. in five hours it isn't actually the same as firing at 500 c. in ten hours. The same amount of heat work has been done, but the material being heated lags in its change on a molecular level in the sense of crystal growth/saturation. I could well be wrong and am interested in a better explanation. It wouldn't be the first time I've been bitten by a 'fond notion'.

True, there can be a difference in crystal growth in glazes, since crystals take time to grow. That's why crystalline glazes need to be held at temperature. But as far as the melt of the glaze is concerned, there will be little difference.

[ayjay]

JoyB, on 08 August 2012 - 08:50 PM, said:

Just looking at my post, it's lost all it's spaces and paragraphs! Not sure how that happened but it looks hard to read so sorry about that!

Joy

This forum does the weirdest stuff sometimes Joy, I tried to read a post this afternoon which had quite a few pics attached, every time I opened a picture it logged me out, when that happens you can't look at another pic until you've logged back in again only to get logged out with the next pic!.

[JoyB]

ayjay, on 09 August 2012 - 03:28 PM, said:

JoyB, on 08 August 2012 - 08:50 PM, said:

Just looking at my post, it's lost all it's spaces and paragraphs! Not sure how that happened but it looks hard to read so sorry about that!

Joy

This forum does the weirdest stuff sometimes Joy, I tried to read a post this afternoon which had quite a few pics attached, every time I opened a picture it logged me out, when that happens you can't look at another pic until you've logged back in again only to get logged out with the next pic!.

Thanks Ayjay, I thought it was just me going daft!

[Mark C.]

Built on a PC for a PC-If you are a mac user like me its always logging me out and changing things. This site reminds me sometimes of the theme lost in space when I compose a post in word and it goes away when I post it.
Mark

[Mark C.]

As others have said its a time temperature deal. The cones measure that to some degree. Cone 10 which is my range on say my glazes is not the same fired in 12 hours as say 16 hours to the same cone 10 end point.The glazes will in the longer fire mature (can run) look better (crystals grow) than the same glazes in a 12 hour fire.Assuming both fires have the same bent cones .
The time thing is a learned over time /experience deal working with your own set of glazes.
Hope this helps.
Mark

[JoyB]

Mark C., on 10 August 2012 - 10:55 PM, said:

As others have said its a time temperature deal. The cones measure that to some degree. Cone 10 which is my range on say my glazes is not the same fired in 12 hours as say 16 hours to the same cone 10 end point.The glazes will in the longer fire mature (can run) look better (crystals grow) than the same glazes in a 12 hour fire.Assuming both fires have the same bent cones .
The time thing is a learned over time /experience deal working with your own set of glazes.
Hope this helps.
Mark

Hi Mark,

Thank you for all your help. I had not realised the revelance of the time or rate of heating the kiln, but when I look back over my firing log it's staring right at me, and I now realise that a fast firing does suit my type of glazes. I use two or more glazes on top of each other with wax rresit and underglazes and fast seems to make them all gel together just fine. One day I will figure out how to post a photo of what I do but it could take a while.

Many thanks Joy