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kevinmansfield

Firing At Cone 05 Instead Of 06

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Hi Folks, 

 

I recently asked a question about my crazing problem using Duncan Envision Glazes. I was advised to try firing at Cone 05 instead of my usual 06 and then slow down the cooling. Unfortunately I have always fired at Cone 06 for my bisque firing and glaze firing and it is only recently I have had the crazing issue. My worry is how the things in the kiln will react. Will I get any warping? Cracking? Or other problems with the bisque? Problems with the glaze?

I tend to use Mayco Stroke and Coat, which says fire to Cone 06 on the bottles and Duncan Envision together on earthenware clay.

 

Many thanks in advance, Kevin.

 

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Many folks working at earthenware temperatures will bisque one cone higher than their glaze temperature. The higher bisque removes more impurities. With a lower glaze, you get less chance of off-gassing from the claybody that can't escape the glaze cover. Maybe try bisque at 05 and glaze at 06.

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In my classroom, I bisque at 04, glaze at 05. I haven't had any issues with glaze defects. Sometimes the glazing comes out looking somewhat bland or even hiddeous, but that may be an application issue on the part of the maker.......

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Guest JBaymore

I've said this one a million times on the forums............ One of the things that you can never get around in studio ceramics is the need to "test, test, test". There are so many variables involved in any given situation that the only way to know for certain is to try it (and try it repeatedly to verify results).

 

best,

 

.................john

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Years ago, I was doing low fire (^06) earthen ware. We were using Amaco glazes at the time. I had always bisqued to ^06, and did then. I had been glaze firing to ^06 also, but found that some of the glazes did not seem to be quite right, and some had some crazing problems. I also noticed that I had a problem with some pin holing on some glazes.  I decided to try different firing cycles, and tested with many witness cones. After all was said and done, I decided to move to ^05, and be cognizant of which glazes needed higher temps and which were in need of cooler ones.  The Amaco glazes used to say 05-06 and I believe that was for ease of labeling as not all of them are 06. Best bet is to become very familiar with your kiln, and with your glazes.

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Many thanks for the replies.

 

I usually fire my bisque and glaze firing together. Will I have any problems if the glaze firing is a higher temperature than the bisque firing? I say this because I have several tiles which I have already bisque fired to Cone 06 and glazed, would it be dangerous to fire these to Cone 05 now?

 

My goal is to eliminate the crazing which I have experienced on my last couple of firings using Duncan Envision glazes and I was advised to try a Cone 05 firing. I currently hold the temperature 998º for 10 minutes, could it be worth holding for longer?

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I used to fire my class kiln , with both greenware and glazed bisqueware together. I don't do this now, if I can avoid it, because it seems that every time I try, something is thicker than it seems, or has an unknown void, which haven't dried, and I end up with bits of bisqueware stuck on the glazed projects.

 

Annnnnnyway, you would not have an issue refiring those tiles. I've refired projects multiple times, to get the glaze to turn out better. I will say, the last firing, a stress crack did appear, so there are limits.

 

In regards to holding, I wouldn't think this would help with crazing, as crazing has more to do with the glaze fit. So instead of holding, you'd be better off slowing the cool down.

The only way to know for sure, is to do what John recommended; test, test, test.

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Guest JBaymore

FYI....... some low fire glazes are sensitive to the gases given off from bisquing clay (like sulphur dioxide) and it can cause glaze defects.

 

best,

 

..............john

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Ditto on what John just said. I never fired the two firings together in those days. Most glazes at the lower range are sensitive to gasses from the bisqueware. Yellows, reds and oranges in particular. It can also effect the blues to some degree making them a little less clean.

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Hi Kevin,

I probably should have mentioned that I have noticed a slight color change at 05 with the Envisions, they tend to darken. These glazes don't move at all, even at 05, and I haven't had any problems with warping or cracking on either a white talc based body (Laguna #10-T). I used a cooling ramp of 250F to 1500F but I'm still testing to see if I can speed that up and get the same results.

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As a newbie I stick to 04 to bisque and 06 to glaze fire on earthenware clay . Never had any problems in my electric kiln .

love reading all feed back from a wealth of experienced potters.

thank you 

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