Paulette Carr on thu 4 nov 99
To my query abut petalite I received and off-line response from Tom Beck:
>Petalite is usually cited as Li2O.Al2O3.8SiO2
>I have seen this analysis: (Weight per cent)
>77% SiO2; 17.5 Al2O3; 0.25 K2O; 0.25 Na2O; 4.3 Li2O; LOI 0.7.
>So it has about half the Li2O that Spodumene has.
>Tom Buck ) tel: 905-389-2339
>(westend Lake Ontario, province of Ontario, Canada).
>mailing address: 373 East 43rd Street,
> Hamilton ON L8T 3E1 Canada
In reading back over the past few digests, I realized that my problem might
be of interest to others working with high fire slip glazes:
I have crazing in my 9 glaze:
my clay body (minus the grog and paper) 50%
wollastonite 40%
petalite
10%.
+ stains or oxides
I was wondering if it was crazing because of a difference in
expansion/contraction: the claybody I use for my sculptures and tiles
contains paper and 30 mesh grog, while the glaze is made from this same clay
body without these two. Since petalite has half the amount of lithium, would
it be helpful to increase the amount of petalite?...or substitute the
petalite for some of the claybody, since it also contains Al2O3 and SiO2?
The glaze seems hard and stable, but the crazing bothers me.
I open this up to all glaze gurus, and to give credit where credit is due, I
got the idea for this slip glaze from an article in Ceramics Monthly by
Joseph Godwin.
Thanks, again!
Paulette Carr
St. Louis, MO
pagcarr@aol.com
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