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## -ron roy - calculating cone 6&10 glazes

### louroess2210 on fri 2 feb 07

On Feb 2, 2007, at 12:55 PM, Ron Roy wrote:

> 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 (than) 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.

Hi Ron, Thanks so much for your explanation .

If I understand it correctly, the following should be true.
Assuming the amount of silica and alumina remain the same, you'll
need more flux to get them to melt at lower temperatures, less flux
for melt at higher temperatures.
Assuming the amount of flux remains the same, lower amounts of
alumina and silica will melt at lower temperatures, higher amounts
need a higher temperature.

Would it also be safe to assume that since there is overlap within
the suggested limits for Cones 6 and 10, unless the numbers are at
one end or the other of the range, you can't really tell by looking
at a glaze whether it would be for cone 6 or cone 10?

Did the reference you cited for the silica and alumina limit formulas
have them for other ingredients, too. If so could you please share
the reference. In the references Ivor gave me the recipes all have
either lead or barium in them and are for cones 2 to 5 or 8 to 12,
nothing about cone 6. Do I just extrapolate?

As you can tell I'm struggling with all this - so much to learn, but
I'm finding my new Glazemaster software to be endlessly entertaining
and instructive.

All the best, Lou

### Ron Roy on sun 4 feb 07

Hi Lou,

First of all - there are many different limit tables - you will find them
in many places - like the Hamer book, Understanding Pottery glazes by Green
and there are many more I am sure.

In GlazeMaster you select the "single recipe compared to limit formulas" in
the "add, edit view recipes" menu on the main menu page. Click on the limit
set and scroll up and down to find the different sets.

They are a starting point - to give you some idea about what range of
oxides will give a good melt at what ever temperature you are working at.
You will develop you own as you use the Seger formula - as we did for
stable glazes in our book. It is a simple mater of looking at glazes and
setting some limits that will tend to give (in our case) a stable glaze. I
have to add - you will find stable glazes out side those limits - so think
of limits as a starting point.

There is a section in our book by the way - different limit sets and an
explanation of how they can be used.

If you have a calculation program you probably already have some. Send me
your fax number and I'll send you the page out of my glaze course book that
has em.

All the programs work the same way in that - as you add flux the numbers
representing alumina and silica go down - just how Seger made it work. The
fluxes add to 1.0 (unity) so it's really the only way it would work.

In the beginning I paid a lot of attention to the limits I could find. Now
I can look at a Seger formula and have a pretty good idea what temperature
a glaze will melt at - and at the same time tell if a glaze is likely to be
over fired. You will see - once you start looking at your glazes through
the unity formula it will all start to make sense. The wild card between
cone 6 and cone 10 is boron or zinc - It is possible to have a lot of
silica or alumina or both if you have a lot of either of those two melters
or a combination.

When I started the only ones I had came with the program I was using - and
there was a range - like cone 3 to 7 - I was still able to start drawing
conclusions use that set.

Hope this is helping Lou - let me know if you need more - why not send me a
recipe you make up according to one of the sets in GlazeMaster and I'll

RR

>On Feb 2, 2007, at 12:55 PM, Ron Roy wrote:
>
>> 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 (than) 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.
>
>
>Hi Ron, Thanks so much for your explanation .
>
>If I understand it correctly, the following should be true.
>Assuming the amount of silica and alumina remain the same, you'll
>need more flux to get them to melt at lower temperatures, less flux
>for melt at higher temperatures.
>Assuming the amount of flux remains the same, lower amounts of
>alumina and silica will melt at lower temperatures, higher amounts
>need a higher temperature.
>
>Would it also be safe to assume that since there is overlap within
>the suggested limits for Cones 6 and 10, unless the numbers are at
>one end or the other of the range, you can't really tell by looking
>at a glaze whether it would be for cone 6 or cone 10?
>
>Did the reference you cited for the silica and alumina limit formulas
>have them for other ingredients, too. If so could you please share
>the reference. In the references Ivor gave me the recipes all have
>either lead or barium in them and are for cones 2 to 5 or 8 to 12,
>nothing about cone 6. Do I just extrapolate?
>
>As you can tell I'm struggling with all this - so much to learn, but
>I'm finding my new Glazemaster software to be endlessly entertaining
>and instructive.
>
>All the best, Lou

Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario