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zno vs calcined zno

updated tue 3 nov 98

 

Grimmer on tue 27 oct 98

Hi,
A friend asked me if there is a chemical change to Zinc Oxide when it is
calcined. Is there a hydrate I don't know about? Neither Hamer nor Magic of
Fire Reference mention any chemical change, only that calcining lowers the
shrinkage of the raw glaze coat caused by the fine particle size. What am I
missing?

steve grimmer
marion illinois.
ps. anyone receive their copies of that new Lark book yet?

Tom Buck on thu 29 oct 98

Steve G:
The zinc oxide of commerce, while being of high-purity (close to
99%), can come from one of four different possible routes (two routes
being dominant). And each process yields a material with different
PHYSICAL properties. And it is this difference in particle size,
"fluffiness", wetability that can cause problems for glaze mixers. By
bringing the ZnO to near fusion conditions (ie, calcining it), one changes
these physical properties to ones more in line with what is needed in a
good glaze slurry (aka slop).

Tom Buck ) tel:
905-389-2339 & snailmail: 373 East 43rd St. Hamilton ON L8T 3E1 Canada
(westend Lake Ontario, province of Ontario, Canada).

On Tue, 27 Oct 1998, Grimmer wrote:

> ----------------------------Original message----------------------------
> Hi,
> A friend asked me if there is a chemical change to Zinc Oxide when it is
> calcined. Is there a hydrate I don't know about? Neither Hamer nor Magic of
> Fire Reference mention any chemical change, only that calcining lowers the
> shrinkage of the raw glaze coat caused by the fine particle size. What am I
> missing?
>
> steve grimmer
> marion illinois.
> ps. anyone receive their copies of that new Lark book yet?
>

Ron Roy on thu 29 oct 98

Hey Steve,
ZnO just loves to soak up atmospheric moisture - all the calcining does is
dry it out again. If it's wet it will get lumpy and even solid. Of course
wet ZnO is diluted so you get less when you weigh it out.

ZnO does not change - not at our temperatures - unless reduced - then the O
part leaves and you have boiling Zn - the metal - probably why ZnO has such
a bad reputation for producing pin holes - RR

>----------------------------Original message----------------------------
>Hi,
>A friend asked me if there is a chemical change to Zinc Oxide when it is
>calcined. Is there a hydrate I don't know about? Neither Hamer nor Magic of
>Fire Reference mention any chemical change, only that calcining lowers the
>shrinkage of the raw glaze coat caused by the fine particle size. What am I
>missing?
>
>steve grimmer
>marion illinois.
>ps. anyone receive their copies of that new Lark book yet?

Ron Roy
93 Pegasus Trail
Scarborough, Ontario
Canada M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849

Web page: http://digitalfire.com/education/people/ronroy.htm

Karen Gringhuis on fri 30 oct 98

Steve - regardless of chemical change ( I think the water is driven
off in the calcining), what you may be missing is that UNcalcined
zinc ox is a bitch to work with - it forms serious lumps which must
be crushed before weighing into a glaze. CALCINED is supposed to be
better and finer & I sure hope this is true. the tests a friend
recently mixed w/ UNcal. were a LOT of work and I didn't think
to get the calcined kind. Karen Gringhuis

RedIron Studios on sat 31 oct 98

Yes it certainly true about uncalcined zinc. My Zinc is a bucket of slightly
smaller than fist sized rocks, and rocks they are. I was mixing some 1000g glaze
tests. I broke my mortar and pestle trying to break these up. I know dumb but I
was getting frustrated. So I have a few questions here...

1) If the Zinc is Calcined how much less do we use 5%,10%,25%.. ?
2) I notice alot of transparents have zinc. Hamers (and others on the list)
have clearly stated this volitzation problem with zinc in reduction. So
what is the biggest reasons to use it. Is there a situation where nothing
in the world but ZnO will do for a particular look/effect?
3) After breaking my mortar and pestle I have decided to really really make a
ball mill a project. From the sounds of the cost of them I guess most people
make
thier own. Does anyone have plans of a ball mill available?

Cheers

-----Original Message-----
From: Karen Gringhuis
To: CLAYART@LSV.UKY.EDU
Date: Friday, October 30, 1998 5:51 AM
Subject: Re: ZnO vs Calcined ZnO


----------------------------Original message----------------------------
Steve - regardless of chemical change ( I think the water is driven
off in the calcining), what you may be missing is that UNcalcined
zinc ox is a bitch to work with - it forms serious lumps which must
be crushed before weighing into a glaze. CALCINED is supposed to be
better and finer & I sure hope this is true. the tests a friend
recently mixed w/ UNcal. were a LOT of work and I didn't think
to get the calcined kind. Karen Gringhuis

Tom Buck on mon 2 nov 98

Since ZnO is high-purity, its LOI is negligible when calcined, and since
the recipe usually calls for ZnO (not ZnO+adsorbed H2O) then calcining
brings the right amount of ZnO to the glaze mix (not that the error is
important, the weight-scale error is bigger).
ZnO is the basis for Bristol glazes, developed 100 years ago as a
sub for lead glazes. Bristols are known for their pastel shades, good
gloss. Zinc oxide is wasted in most C10 reduction glazes, espy those
needing heavy reduction. When ZnO is changed to Zn metal at 1200 C, the
metal immediately goes to vapour and up the flue.

Tom Buck ) tel: 905-389-2339
& snailmail: 373 East 43rd St. Hamilton ON L8T 3E1 Canada
(westend Lake Ontario, province of Ontario, Canada).