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## calculating cone 6&10 glazes

### louroess2210 on tue 30 jan 07

Hi everyone,

In glaze calculation, what are the differences between a cone 6
glaze recipe and one for cone 10? Is the coeffecient of expansion
different? What about the SiAl ratio.
Mastering Cone 6 Glazes gives some good guidelines for Cone 6 but
I'm having trouble finding information on cone 10. Are the oxide
limits the same? Is it the amount of flux and/or the kind of flux
material used that makes the difference? Can you tell by looking at
the recipe if it's for 6 or 10?
Thanks for any help.

### Ivor and Olive Lewis on thu 1 feb 07

You ask <6 glaze recipe and one for cone 10? Is the coeffecient of expansion =
different? What about the SiAl ratio.>>

I suppose the first consideration is to reduce the proportion of Fluxing =
(R2O) agents in relationship to the combined quantity of Silica and =
Alumina (SiO2/Al2O3) going up to cone 10 or increase them going down to =
cone 6. This can be seen if you look at the analysed composition of =
Seger Cones where the ratio between SiO2/Al2O3 remains (almost) constant =
but increases with increasing maturity temperature.

The second point to consider is Chemical Activity. There are some glazes =
that will not give spectacular results at lower firing temperatures =
because the chemicals responsible for the effects do not begin to =
decompose until their temperature rises towards or beyond Cone 10.

Oxide Analysis of Seger Cones was often used as a starting point for a =
glaze series before the advent of computer assisted glazing. The rule of =
thumb was to use, as a base glaze, the analysis of a cone that was four =
or five steps below the one you intended using. Using the Seger Table =
and considering firing at Orton Cone 6 (1200 deg C), then, for a clear =
glaze the Seger cone 1a (1100 deg C) Analysis would be; K2O 0.3, CaO =
0.7, Al2O3 0.3, Fe203 0.2, SiO2 4.0.

For compilations of glaze limits see D. Rhodes, "Clays and Glazes for =
the Potter" (P 166-8) or Glen C. Nelson, "Ceramics, a Potter's Handbook" =
(P 201).=20

Finally, always remember that Time and Temperature have a degree of =
Elasticity. In some situations extending time at a lower temperature can =
deliver the same amount of work energy as a shorter time at a higher =
temperature. So firing schedules must be considered when constructing =
or designing a glaze.

Ivor Lewis.
Redhill,
South Australia.

### Ron Roy on fri 2 feb 07

Hi Lou,

First of all - Neither heat expansion/cooling contraction or Silica/alumina
ratio have anything to do with when a glaze melts.

You can raise and lower the expansion of any glaze whether it is a low fire
or a high fire glaze.

Same with silica/alumina ratio - nothing to do with temperature. If the
silica alumina ratio of a glaze is 10.0 - all that means is there is 10
times the amount of SiO2 compared to one part of Al2O3.

Because cone 10 is a higher temperature than cone 6 - you will need less
fluxing material to melt at cone 10 - remember - you are melting silica and
alumina to make glazes. As a general rule you will find the amounts of SiO2
and Al2O3 higher in cone 10 glazes and in cone 6 glazes.

In one set of limit formulas for instance they suggest 0.275 to 0.65 for
Al2O3 and 2.4 to 4.7 SiO2 are recommended limits for cone 6 glazes.

For cone 10 glazes they suggest 0.45 to 0.825 Al2O3 and 3.5 to 6.4 SiO2.

Hope that clarifies things - just remember - one way of lowering the
melting temperature of a glaze is to lower alumina and silica - to make it
easier to melt.

RR

>Hi everyone,
>
> In glaze calculation, what are the differences between a cone 6
>glaze recipe and one for cone 10? Is the coeffecient of expansion
>different? What about the SiAl ratio.
> Mastering Cone 6 Glazes gives some good guidelines for Cone 6 but
>I'm having trouble finding information on cone 10. Are the oxide
>limits the same? Is it the amount of flux and/or the kind of flux
>material used that makes the difference? Can you tell by looking at
>the recipe if it's for 6 or 10?
> Thanks for any help.
>
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Ron Roy
RR#4