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calcined alumina?

updated tue 15 jul 03

 

Judi Buchanan on sun 13 jul 03


The term "calcined alumina" is used in a Ravenscrag glaze recipe. I am
not familiar with this term. I know alumina's source is clay. Does it
simply mean calcined clay?

Judi Buchanan

Kendall deaton on mon 14 jul 03



Calcined alumina is Alumina Hydrate that has been fired to Cone 06 or so ( in a bisque bowl or some other open form). This drives off the the chemically combined water. Be careful it is a very fine powder afterwords(wear your dust mask).


Kendall


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Snail Scott on mon 14 jul 03


At 10:25 PM 7/13/03 -0500, you wrote:
>The term "calcined alumina" is used in a Ravenscrag glaze recipe. I am
>not familiar with this term.


I'm guessing that one could use alumina oxide.
(Just not alumina hydrate.)

-Snail

Judi Buchanan on mon 14 jul 03


Thanks, that brings up another question. Why calcine alumina? Does it
improve the unfired glaze or the fired product?

Judi Buchanan



-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG] On Behalf Of Kendall
deaton


Calcined alumina is Alumina Hydrate that has been fired to Cone 06 or so
( in a bisque bowl or some other open form). This drives off the the
chemically combined water. Be careful it is a very fine powder
afterwords(wear your dust mask).

Kendall




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Kendall deaton on mon 14 jul 03



Calcining the alumina hydrate makes it much less reactive to fluxes, therefore raising the maturation temperature of lower melting glaze materials. It makes the glaze more viscous and less likely to run. It also makes the surface of the glaze tougher before firing. Using calcined alumina in a glaze makes it much more prone to settling so add bentonite at 2% or 3%.


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