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firing cone 5 clay with cone 6 glazes


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hi first post here but read these forums a lot! I have a couple light colored laguna cone 5 clay bodies and have made cone 6 glazes using John Britt’s mid-fire glaze book. So what cone should i be firing to? Would soaking at 5  instead of firing all the way up to 6 make a difference for the clay body or do I still run the risk of over-firing the body? Are there stability consequences for under-firing my glazes to cone 5, or would the difference only be visual? Should I just compromise and aim for 5.5? I hear this combination of clays and glazes is normally not an issue but I’m not sure where to start since all my firing knowledge is theoretical at this point. Just bought an electric kiln and have never fired by myself before! I know testing is the answer, but I’d like to go in as informed as possible. 

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Everything you just said is a possibility. If your clay body can handle cone 6, then fire to 6. You'll have to test it to know for sure. If it can't handle it, then fire to cone 5. If the glaze doesn't melt as much as you'd like at 5, increase the frit or Gerstley Borate in the recipe by a couple percent to increase the melt. Cone 5 with a 10 minute hold will get you to cone 5.5, and that may be a great solution, too. Test, test, test.

What clay body are you using? Someone here may have experience with it.

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thanks for the quick reply! I’m using Hagi porcelain and Weststone II. 

When testing, I’m under the impression that the load size is a variable to be controlled, so I should still be firing the kiln full (it’s only 18” x 18”), yes? or is this variable too minor to factor in with when testing such a large variable as cone 5 versus 6? thanks!!

 

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I have not used either of those Laguna clays.  For the most part, Laguna does have their clay bodies dialed in, but like Chilly and Neil said, you are going to have to test in order to know.  Sometimes my test pieces are just that, pieces I have trimmed through the bottom or have some flaw and I glaze them.   Better information at times than a small test tile.  I fire to cone 6 with Laguna Speckled Buff, #16 porcelain, and RSMC.  My glazes are all mid fire range that I mix myself.  What glazes out of John's book did you mix?  You may have to consider this first load a test load.  You could start with cone 5 and check your results.  If it's not what you hoped for, you could refire or remake and fire to cone 6?  Just a thought.  I know it is redundant, but you will have to test.  A lot.  

Roberta

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On 4/14/2021 at 7:48 AM, Roberta12 said:

I have not used either of those Laguna clays.  For the most part, Laguna does have their clay bodies dialed in, but like Chilly and Neil said, you are going to have to test in order to know.  Sometimes my test pieces are just that, pieces I have trimmed through the bottom or have some flaw and I glaze them.   Better information at times than a small test tile.  I fire to cone 6 with Laguna Speckled Buff, #16 porcelain, and RSMC.  My glazes are all mid fire range that I mix myself.  What glazes out of John's book did you mix?  You may have to consider this first load a test load.  You could start with cone 5 and check your results.  If it's not what you hoped for, you could refire or remake and fire to cone 6?  Just a thought.  I know it is redundant, but you will have to test.  A lot.  

Roberta

I’ve mixed up a kaki, an oil-spot temmoku, John’s nuka, a magnesium matte, and a clear that’s replicated from mastering cone 6 glazes. I know oil- spots will need to get up to at cone 6 to form, not sure how flexible the others are or aren’t. I bought a small kiln knowing that my entire practice is one big test, but i appreciate hearing how others approach test loads. thanks! 

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