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I was loading a glaze kiln and because I still had some room, I decided that I would single fire a couple bowls. I've never single fired.

My concern is that I used an underglaze with CMC in it and then dipped them in a clear glaze. Just small areas of underglaze with CMC. I was using stencils and wanted the underglaze to stay put.

Was it wrong to put glaze on top of an underglaze with CMC and then just single fire? Should I just fire and see what happens? What could happen? I plan to fire to cone 6.

Thank you,

Betty

Edited by Bam2015
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Single firing is usually no different EXCEPT that it is really just a bisque firing to glaze temperature. The raw clay body needs to be fired slowly during the early stages so that it does not explode or fracture. Bisque schedules usually provide for this; glaze schedules for previously bisqued ware just charge ahead, damn the torpedoes. The glaze work itself is just fine, it's the clay body that you need to worry about.

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Dick, thank you for your response. My concern is the CMC in my underglaze with the single firing. Doesn't CMC burn out? And if so, how will that affect the clear glossy glaze that I put over it? 

Maybe I just have to start my kiln and see what happens.

What do you mean when you say it is the clay body that I have to worry about? 

Betty

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The CMC will burn out early. Clay body is the term we use for the raw clay that you made the piece with. The raw clay molecule has 2 forms of water in it that must be dealt with carefully during the first 1000 degrees of the first firing, whether bisque that will be fired again with glaze, or single firing that will go from zero to cone 6 in one firing.

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Some underglazes don't take dipping glazes very well unless you bisque fire them before glazing. Speedball underglazes are like that. If it looked like your glaze covered well when you applied it, then things will be fine unless you fired too fast for your clay and glazes liking. The problem is that if you go too fast, the glaze starts to melt before there has been sufficient time for the organics to burn out of the clay, and those gasses can get trapped in the clay and cause bubbling.

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14 hours ago, neilestrick said:

Some underglazes don't take dipping glazes very well unless you bisque fire them before glazing. Speedball underglazes are like that. If it looked like your glaze covered well when you applied it, then things will be fine unless you fired too fast for your clay and glazes liking. The problem is that if you go too fast, the glaze starts to melt before there has been sufficient time for the organics to burn out of the clay, and those gasses can get trapped in the clay and cause bubbling.

Neil, thank you for chiming in. Your responses are always spot on. 

Old Lady, I will share results. 

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Hi All,

I said that I would report back after I single fired pots with CMC in the mason stain mix. The glaze seemed to resist some areas where I used the CMC/Mason stain mix. If I am using underglazes or mason stains with CMC added, then I won't be single firing. Sorry, no pics to share, busy working at my paying job. 

Betty

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On 8/3/2022 at 3:15 PM, Bam2015 said:

I was loading a glaze kiln and because I still had some room, I decided that I would single fire a couple bowls. I've never single fired.

Just asking if you used your normal glaze fire program since the kiln was packed with typical glazed ware or did you slow it down and fire on a bisque schedule but to your planned glaze temp?

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On 8/5/2022 at 4:29 PM, neilestrick said:

Some underglazes don't take dipping glazes very well unless you bisque fire them before glazing. Speedball underglazes are like that. If it looked like your glaze covered well when you applied it, then things will be fine unless you fired too fast for your clay and glazes liking. The problem is that if you go too fast, the glaze starts to melt before there has been sufficient time for the organics to burn out of the clay, and those gasses can get trapped in the clay and cause bubbling.

Neil, do you use underglaze on just greenware or sometimes on Bisque?  If on bisque, do you refire once you put underglaze on?  

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On 8/3/2022 at 1:15 PM, Bam2015 said:

I used an underglaze with CMC in it and then dipped them in a clear glaze. Just small areas of underglaze with CMC

From this I would assume you are using an underglaze that contains CMC?

But then, from the quote below it sounds like it could have been CMC + stains?

3 hours ago, Bam2015 said:

The glaze seemed to resist some areas where I used the CMC/Mason stain mix.

Could you clarify what you used that had the glaze resist some areas as CMC + stain doesn't equal an underglaze.

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1 hour ago, Roberta12 said:

Neil, do you use underglaze on just greenware or sometimes on Bisque?  If on bisque, do you refire once you put underglaze on?  

I do all my underglaze work on greenware (the dry side of leather hard), because I also do mishima work on everything, which requires the pot to be soft enough to carve lines. Plus the underglazes I use (Speedball) take glaze better if they've gone through a bisque firing. If I wasn't doing mishima I'd apply my underglazes at bone dry, because they dry faster than at leather hard and you can wipe/scrape off mistakes much easier than on bisque. On bisque some colors will stain the clay enough that you can't get it completely clean.

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2 hours ago, Bill Kielb said:

Just asking if you used your normal glaze fire program since the kiln was packed with typical glazed ware or did you slow it down and fire on a bisque schedule but to your planned glaze temp?

Bill,

I used the 'slow glaze' program and fired to cone 6 in my L & L kiln. I like to keep things simple. 

Betty

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1 hour ago, Min said:

From this I would assume you are using an underglaze that contains CMC?

But then, from the quote below it sounds like it could have been CMC + stains?

Could you clarify what you used that had the glaze resist some areas as CMC + stain doesn't equal an underglaze.

Min,  I brushed the outside of the pots in underglaze (no CMC mixed in). I then added designs using stencils. In the stenciled areas I used Mason stains mixed with CMC. I used the CMC thicken the Mason stain mix so it would be less likely to seep under the edges of the stencils. 

I hope that made sense. Sorry if I confused anyone.

Betty

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34 minutes ago, Bam2015 said:

Min,  I brushed the outside of the pots in underglaze (no CMC mixed in). I then added designs using stencils. In the stenciled areas I used Mason stains mixed with CMC. I used the CMC thicken the Mason stain mix so it would be less likely to seep under the edges of the stencils. 

I hope that made sense. Sorry if I confused anyone.

Betty

Got it. If it's worked before this way then perfect. I was just wondering if you used one of the refractory stains (like the chrome greens) as that can cause a rough unglazed texture if a flux isn't added to it.

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12 minutes ago, Babs said:

Was the stencil area totakly dry?

CMC dries slowly, glaze won't take up in those areas if still damp compared to other areas and so will show in the firing.

That’s a really interesting point. To build glaze up over heavy underglaze, I spray multiple coats and air dry the heavy underglazed areas with the spray gun “air only”  to dry for the next coat because they do not take up the glaze. I am not sure how you could achieve that dipping or even brushing ought to be difficult.

Edited by Bill Kielb
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5 hours ago, Bill Kielb said:

That’s a really interesting point. To build glaze up over heavy underglaze, I spray multiple coats and air dry the heavy underglazed areas with the spray gun “air only”  to dry for the next coat because they do not take up the glaze. I am not sure how you could achieve that dipping or even brushing ought to be difficult.

Also Bill, the porosity of the surface will change when CMC is used imo

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