[Clayart] A weak stew

ronroy at ca.inter.net ronroy at ca.inter.net
Wed Apr 11 12:26:14 EDT 2018

Hi Douglas,

We go into this a lot in our book. How we tested the glazes and the  
criteria we used.

The "rules" we came up with are:

1&2. Get enough silica and alumina into the glaze
3. Make sure the glaze is well melted
4. Don't overload colouring oxides - especially copper

If SiO2 (silica) is below 2.5 then you can suspect an unstable glaze.  
Same with Al2O3 (alumina) when below 0.25.

We know there are stable glazes - even well out of these parameters  
but if you wanted some guidelines to make stable glaze these would  
serve well.

We only tested at cone 6 but we believe the results are applicable to  
other temperatures as well.

You can still buy it as an ibook or as a black and white single  
publication with the colour photos on our web site.



Quoting Douglas Fur <23drb50 at gmail.com>:

> Ron
> Just for the sake of clarity what parameters means "not enough silica or
> alumina"?
> [For starters I copied this one and I'm not sure if it is the one you
> referred to as out of balance or your revised version...]
> Are there reasonable rule of thumb numbers here, such as SiO2>2.0 and
> Al2O3:SiO2 at 1:10?
> (There was a glaze on clay buddies the other day with SiO2 @1.5, Al2O3
> @.15, and B2O3 at .15 which seems scantier.)
> Also ZnO at .31 seems like a bit much vis RO at .86 and R2O @ .14
> How do you read these numbers?
> Duff
> Seola Creek
>> 0.33* CaO
>>> 0.22* MgO
>>> 0.04* K2O
>>> 0.10* Na2O
>>> 0.31* ZnO
>>> 0.00  Fe2O3
>>> 0.00  TiO2
>>> 0.10  B2O3
>>> 0.15  Al2O3
>>> 1.85  SiO2
>>> Si:Al:  12.12
>>> SiB:Al:  12.76
>>> Thermal Expansion: 484.50
>>> Formula Weight: 196.24
>>> RR

Ron Roy
ronroy at ca.inter.net
Web page ronroy.net

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