Mary Lynch on sun 17 dec 00
Tom Buck wrote:
> Shimmer with Li2CO3 just gets into the ballpark as a serviceable
> glaze. It needs at least Cone 5,better at C6. It needs to get some silica
> from the body so it will work better on white bodies rather than dark
> ones. When this cools after firing and soaking, it will be a satin matt
> most likely. Not sure how much the Rutile will affect the blue of cobalt;
> streaking it, yes, but what else? The glaze should be foodsafe but it
> would be worthwhile to have it tested for release of lithium and cobalt.
> Shimmer with SrCO3 turns this mix into a "calcium alumina matt"
> the alkaline earth metals, Ca, Sr, Mg, as oxides, total 77% of the flux
> (melting) oxides, so it becomes a true Cone 6/7 glaze, and will be satin
> matt for sure. Again, the body and firing regimen will make a major
> difference in colour and motling. If fired to C7 and soaked it should be =
a
> smooth satin matt, and durable.
Tom,
I appreciate you taking time to look at this glaze and am learning so much
from the responses you and others have taken the time to post. Your comment=
s
confirm my experience so far with this particular glaze. I fire to ^6 and
soak for 45 min., and the cones are bent completely. The color and surface
are more interesting than most blues and it enhances textured surfaces if
not too thick.
I had begun testing this glaze in the microwave, etc. and agree that testin=
g
for lithium and cobalt would be in order.
For anyone else who would like to test this glaze, here is the formula:
=B3SHIMMER=B2 ^4 - 8 OX.
Custer spar 45.0
whiting 22.0
silica 13.0
china clay 14.0 (I used EPK)
lithium carb. 6.0 (I used strontium, 3/4 the amount
of lithium)
+
rutile 6.0
cobalt carb. 2.0
bentonite 1.0
If the glaze is thin it is an inky, translucent blue; if thick it=B9s a satin
matt with quite a bit of nice surface variation. (I like it thick)
I fired to a hot cone 6: programmed my Skutt for a medium speed ^6 with a
45-min. soak at the end. I haven=B9t tested it at higher or lower temps yet.
Supposedly it goes green at higher temp, described as =B3not nice.=B2 (?)
Looks approximately the same on all 3 clay bodies tested, except the color
is a bit brighter on white clay. (Tested on Highwater's Speckled brownstone=
,
Ellen's Buff, and ^5 porcelain)
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