Linda Pahl on thu 12 feb 04
Hi, Bruce.
Thanks very much for your help with the reformulation and for your
explanatory comments. It is good to finally understand how to properly
sub strontium for lithium.
I have forwarded your post to Denise; she will test the new recipe next
week and will report back with her results.
Thanks again!
Linda
> Linda,
> If your friend replaces half the lithium with double that % of
> strontium carb the Unity Molecular Formula will be the same in terms
> of the ratio of flux to stabilizer to glass former. In numbers, use 4%
> lithium carb, 8% strontium carb.
>
> HOWEVER, the glaze will not necessarily look the same, and the
> shivering may not disappear. Here's why. As you indicate, lithium
> influences color response of the cobalt. Removing some may change the
> hue of the cobalt.
>
> More important is the shivering. The recipe posted is for a glaze with
> a fairly high expansion, despite the lithium present. But shivering
> comes when the expansion of the glaze is lower than the expansion of
> the clay body. So what's happening here? I can only speculate but it
> appears the somewhat water-soluble lithium ions are drying on the rim
> of her ware, and causing localized low expansion of the glaze, hence
> shivering there. I have no idea whether cutting the lithium from 8 to
> 4% will cure that entirely. And shivering is a fault she wants cured,
> totally. Removing all the lithium carb, and using 16% strontium carb
> keeps the UMF ratios the same, so that's another point to test.
>
> So the caveat is, this is a starting point for further testing, not a
> guarantee of a cure.
>
> Good city potting,
>
> Dave Finkelnburg, in a very small town in Idaho but gratefully blessed
> with more room to throw in than just the space in the hall closet!
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