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PaulR

Bisque/Glaze Firings

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I just finished a bisque firing where I had used stains and underglazes on greenware.  They came out exactly like I wanted so I do not need to do anything else to the pots.  Is it ok to immediately start the glaze firing?  Is it better for the pots or the kiln to be completely cool?  The kiln reads 100 degrees, will that hurt if I start the glaze firing?

Thanks for any advice.

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It's fine to start the kiln while still warm. Going forward, if you are not glazing you can single fire (bisque and glaze in one firing) and go to whatever cone you are "glaze" firing to. This type of single firing goes slow like a bisque up to your bisque cone/temperature then proceeds with the remaining firing going at the schedule for the glaze firing from the peak temperature of your bisque to your final "glaze" cone/temperature. Do you have a programmable controller or a manual kiln and what cone are you firing to?

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It's an Easy fire automatic L&L kiln and I fire to cone 6.

I tried letting some pots dry longer and then fired them at cone 6 with no bisque firing and they all blew up.  They seemed completely dry so not sure why.

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2 hours ago, PaulR said:

It's an Easy fire automatic L&L kiln and I fire to cone 6.

I tried letting some pots dry longer and then fired them at cone 6 with no bisque firing and they all blew up.  They seemed completely dry so not sure why.

Moisture in the pots will cause them to blow up. Put a room temperature pot against your cheek and if it feels cool on the bottom then it's still not dry. If you used a cone 6 glaze firing program it likely went too fast through the lower temperatures. There are charts here showing what the ramps are using the controllers that are on the L&L kilns. If you do a mash up of a ^04 bisque with an average ^6 glaze program you would have something like this:

(all in F)

80 / 250 / hold for 2-3 hours if you are not sure the pots are dry or if they are thicker than 3/8" or so

200 / 1000 / 0 hold

100 / 1100 / 0 hold

180 / 1676 / 0 hold (from here on it goes to the latter part of a med/fast ^6 glaze firing schedule)

400 / 2000 / 0 hold

108 / 2130 or until cone 6 is down

kiln off

 

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Is there any advantage to leaving a vessel unglazed?  I did try this and found that the surface scratched very easily. How could I avoid this happening?  I did glaze the inside, my thinking being that if the vessel were to be used for food purposes then it would be food safe. I do like the look of a matt unglazed surface. A pic of a local potter's bowl is attached.

 

Thanks

40003602_2188257624778024_597770322736840704_n.jpg

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On 9/17/2018 at 4:45 PM, AndreaB said:

Is there any advantage to leaving a vessel unglazed?  I did try this and found that the surface scratched very easily. How could I avoid this happening?  I did glaze the inside, my thinking being that if the vessel were to be used for food purposes then it would be food safe. I do like the look of a matt unglazed surface. A pic of a local potter's bowl is attached.

 

Thanks

40003602_2188257624778024_597770322736840704_n.jpg

It sounds like your pots might not have been vitrified. What cone is your clay vs the firing that you did?

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PAUL R,  is there an electronic controller on your L&L?      there is a preheat section on mine and i use it all the time because i single fire.   i am not suggesting that you single fire but if you do have a controller, try the preheat with a hold time of an hour to thoroughly dry your work before the temperature rises.    then try slow glaze to the cone you wish.  just to see if that will work.

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On 9/16/2018 at 8:10 PM, PaulR said:

 

 They seemed completely dry so not sure why.

 

 

How thick were they? 

Did they have enclosed hollow areas?

 

 

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On 9/23/2018 at 8:50 PM, Rebekah Krieger said:

It sounds like your pots might not have been vitrified. What cone is your clay vs the firing that you did?

I bisque fire to 1000 deg C and glaze fire to 1222

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