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I just did a cone 06 bisque fire. Normally runs 11 1/2 to 12 hours and then cone sitter shuts it down.  Yesterday it shut off after 8 hours??!! Just wondering how a person knows if the pieces are fired enough, or should I redo it or??? Can you help me out?

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Rockhopper    11

Lots of variables...   some additional information will help you get better answers:

Is it a manual kiln, or is there a programmable controller? Did the sitter 'trip', or did it shut off before that ?  Any witness cones ?  What did they look like ?  How full was the kiln ? (Was there more, or less in it than "Normal" ?)

 

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The kiln is a manual switch. Five switches, one hour apart. I turned the last switch on at 5:30.  So only 3 hours from the last switch to shut off. The sitter tripped. It was a full load. Most pieces appear to be as normal. I had a bowl on the top shelf that I had done a stained slip design on that the colours didn't pop like I was expecting, so that was kind of why I was questioning it.

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Min    783

Did you use less shelves in this load, taller pieces, less mass? New elements?

If you didn’t have a witness cone to verify the sitter cone/bar does the bisque look the same colour as bisque that took the longer firing? Another thing you could do is touch the tip of your tongue to a piece of old bisque and then a piece from the fast firing load. Does the new stuff make your tongue stick to it more than the old? (who said potters are a little goofy?) Or, you can place a drop of water on the old bisque and count how long it takes to soak into the clay and then try that with your fast fired bisque. Your slips won’t pop until they have a cover coat of glaze so I wouldn’t go by that. If you are unsure you could always re-bisque the load and use a witness cone to monitor the firing.

Porcelain and white clays have less carbon and gunk to burn out than darker clays, which do benefit from having a longer and slower bisque. Pinholes and blisters in a glaze fire are often from gasses burning out through the glaze that didn’t have either the time or the venting to burn out during the bisque. So the type of clay you used can make difference in your bisque schedule.

These are the firing profiles for the fast and slow bisque for the Bartlett controller going to ^04. 

 

bisque profiles.png

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The bisque is the same colour as ever. Used an M340 clay. So I put a drop of water on old bisque and it took 35 seconds to absorb. The new bisque absorbs almost immediately.  What's my options?? Go with it, or re-fire or??? Nothing changed in this bisque firing from any others I've done. And no, I didn't have any test cones, which I will in the future. I usually learn the hard way. 

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Min    783

If they were my pots I would re-bisque. They are going to soak up the glaze much faster and probably result in it going on too thick otherwise. Also run a higher risk of glaze pinholes/blisters. Tongs could break really underfired bisque too.

Before the next firing I would check the sitter adjustment. Starting at 2:47 in this video it shows how to do this. Do you have a timer on the kiln that shut the kiln down prematurely? 

https://www.youtube.com/watch?v=8wo5W3vI8Ec

 

 

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