Erin Hayes on fri 31 jan 97
Anyone know to what temperature one would calcine zinc oxide? My student
Mike is testing some Oxblood glazes we snagged off the listserv and all
of them that have zinc ox call for calcined zinc ox.
Anyone have any ideas on the advantage of using it calcined instead of raw?
Erin.
%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%
Erin Hayes, Art/Humanities Instructor Voice mail: (509)574-4844
Yakima Valley Community College School e-mail:ehayes@ctc.edu
PO Box 1647 Home e-mail:TXGirlNWA@aol.com
Yakima, WA 98907-1647 "Clay is Good."
%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%#%
Craig Martell on sat 1 feb 97
At 08:18 AM 1/31/97 EST, you wrote:
>----------------------------Original message----------------------------
>Anyone know to what temperature one would calcine zinc oxide? My student
>Mike is testing some Oxblood glazes we snagged off the listserv and all
>of them that have zinc ox call for calcined zinc ox.
>
>Anyone have any ideas on the advantage of using it calcined instead of raw?
>
>Erin.
>
Hi Erin: Raw zinc will shrink a lot early on in firings and sometimes cause
the glaze to crawl. Calcining will fix the problem. I used to calcine zinc
to cone 06 which is my bisque temp. and that is plenty. If you glazes only
call for small amounts of zinc, say 2 to 5%, I wouldn't worry about doing
the calcining. That isn't enough zinc to cause a problem IMHO.
Regards, Craig Martell-Oregon
Ron Roy on mon 3 feb 97
>----------------------------Original message----------------------------
>At 08:18 AM 1/31/97 EST, you wrote:
>>----------------------------Original message----------------------------
>>Anyone know to what temperature one would calcine zinc oxide? My student
>>Mike is testing some Oxblood glazes we snagged off the listserv and all
>>of them that have zinc ox call for calcined zinc ox.
>>
>>Anyone have any ideas on the advantage of using it calcined instead of raw?
>>
>>Erin.
>>
>
>Hi Erin: Raw zinc will shrink a lot early on in firings and sometimes cause
>the glaze to crawl. Calcining will fix the problem. I used to calcine zinc
>to cone 06 which is my bisque temp. and that is plenty. If you glazes only
>call for small amounts of zinc, say 2 to 5%, I wouldn't worry about doing
>the calcining. That isn't enough zinc to cause a problem IMHO.
Just a word of cauction - above 950C (1742F) zinc oxide is very easily
reduced. The released carbon in a bisque kiln, if still around, will reduce
the ZnO to Zn and boil off. I would weigh the ZnO before calcining and
after - the difference in weight could make a difference to certain glazes.
If you know the difference in weight you can then allow for it.
I am also assuming that, if not stored in airtight containers the ZnO will
gradually rehydrate and need recalcining.
Ron Roy
Toronto, Canada
Evenings, call 416 439 2621
Fax, 416 438 7849
| |
|
