Robert Galejs on tue 6 apr 04
On our quest for white porcelain, we have tried a couple of porcelain
and bone china casting slip formulations. The test pieces with higher
proportions of silica are yellower. Thus, it appears that the silica
may be causing some of our non-whiteness issues. We used 325 mesh flint
silica from Laguna Clay. Would anyone have a source for a whiter-firing
silica? Searching on the Web, I found a brand of silica called
sil-co-sil that claims to be very white, but I don't know if it really
is. Anyone tried this?
Thanks,
Robert Galejs
mailtoandrew@FSMAIL.NET on thu 8 apr 04
Hello Robert,
First the easy one ... Sil-co-sil is a very high purity silica with low
Fe2O3 and TiO2, typically about 0.017% and 0.01% respectively. It should
not be detrimental to a high degree of fired whiteness.
You state that ... the test pieces with higher proportions of silica are
yellower. Thus, it appears that the silica may be causing some of our non-
whiteness issues. Just a thought but as fired whiteness is effected by the
maturity of the body have you allowed for the increased refractoriness of
the bodies with increased silica?
Regards,
Andrew
Robert Galejs on thu 8 apr 04
mailtoandrew@FSMAIL.NET wrote:
> Hello Robert,
>
> First the easy one ... Sil-co-sil is a very high purity silica with low
> Fe2O3 and TiO2, typically about 0.017% and 0.01% respectively. It should
> not be detrimental to a high degree of fired whiteness.
>
> You state that ... the test pieces with higher proportions of silica are
> yellower. Thus, it appears that the silica may be causing some of our non-
> whiteness issues. Just a thought but as fired whiteness is effected by the
> maturity of the body have you allowed for the increased refractoriness of
> the bodies with increased silica?
>
> Regards,
>
> Andrew
Andrew -
Good to hear about the Sil-co-sil. I have a sample on order and will
see if that makes a difference or not.
Until we receive that, we have been testing out procelain-bone china
hybrids with varying amounts of bone ash, silica and kaolin. We have
been varying the cone number according to the relative proportions of
bone ash and silica (more bone ash lowers firing temp and more silica
raises it) The final results appear to be well fired (according to my
wife) and all have similar shrinkage.
Thanks,
Robert
| |
|
