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Cone 6 Silica, Alumina, Flux Ratio


srnadine

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Hesselberth and Roy, in Mastering Cone 6 Glazes, give a pretty good treatment of the ratio between silica and alumina.  They also discuss which fluxes work, in their opinion, at cone 6.  They also acknowledge there are many variables.  In Appendix I, they offer a Seger molecular limit range of 0.25 to 0.5 for alumina and 2.5 to 4.0 for silica.  They also state that a silica to alumina ratio of 7:1 or higher will be glossy and a ratio of 5:1 to 7:1 will be matte, with an alumina matte at a ratio of 4:1.  

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I recently downloaded the free version of Insight (I'll probably end up buying it) and that glaze calculation program is a great source of inspiration.  You can analyze any number of glazes and see what the oxide ratios actually are... gives you a really helpful insight into real-world glaze chemistry.

 

It's been especially helpful to me at this point in time, because I'm an episodic potter.  I hadn't made any pots for several years, and in the last fallow period, my kiln and glaze room developed a roof leak that I didn't notice until my notebooks were destroyed.  So while I still have a lot of glazes I can use, I don't remember exactly how I made them.  It's new glaze time for me, which is good.  But I fire at Cone 8, which is awkward, since most published porcelain glazes fall into either 6 or 10.  I can use the program to compare two glazes of similar intent in 6 and 10, and try to work out an oxide balance that might work at 8.

 

So far so good!

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I recently downloaded the free version of Insight (I'll probably end up buying it) and that glaze calculation program is a great source of inspiration.  You can analyze any number of glazes and see what the oxide ratios actually are... gives you a really helpful insight into real-world glaze chemistry.

 

It's been especially helpful to me at this point in time, because I'm an episodic potter.  I hadn't made any pots for several years, and in the last fallow period, my kiln and glaze room developed a roof leak that I didn't notice until my notebooks were destroyed.  So while I still have a lot of glazes I can use, I don't remember exactly how I made them.  It's new glaze time for me, which is good.  But I fire at Cone 8, which is awkward, since most published porcelain glazes fall into either 6 or 10.  I can use the program to compare two glazes of similar intent in 6 and 10, and try to work out an oxide balance that might work at 8.

 

So far so good!

 

I fired at cone 8 for a couple of years, and it was super simple to drop everything down to cone 6, like a couple percent of Gillespie Borate. Your kiln elements will thank you.

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Guest JBaymore

Get the Level II Insight... the access to info is well worth it.

 

That is the "required text" for the ceramic materials courses I teach at the college.

 

best,

 

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

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John, with the 40% off that's a good deal, I think.

 

Neil, I know you're right, but I just haven't found a porcelain that I like at 6.  At 8, the Standard 130 I use has that highfire density, decent translucence, and throws well enough.  And when I come up with my next fuel burner, the body holds up pretty well to higher heat; I've fired it to 11-12 in a woodburning groundhog with no issues.  We have a little farm in upstate NY, and I've been thinking about building a fastfire wood kiln up there.  Or at least an oil burner, which I like a lot too.  (Right now we're in FL; it hasn't gotten above freezing at the farm for two months.  I'm too old and feeble for that nonsense.)

 

Yeah, I'm probably a materials snob, among my many other flaws.  I've been considering starting a thread about the nobility of materials... please talk me out of it.

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