Vikki Dow on thu 5 apr 01
We revised the old Floating Blue using Cadycal and Frit 3134 to replace
gerstley borate and have used two batches of this glaze over the past 6
months. Kiln loads have been pretty consistent. Well, now all hell is
breaking loose. First we mixed up 30 pounds and fired a load to have it all
turn BLACK with pinholing. We could only deduct that somehow we left
something out by accident (any ideas???).
Now, after mixing up a new batch, we fired a test and it came out fine.
Fired a whole kiln load and it is not fine anymore! Instead of a rich,
vibrant blue, it is a dull grey-blue. We are totally stumped. And
overwhelmed, as the whole kiln load was supposed to be sent out to galleries
tomorrow! ANY ideas on what is happening here would be greatly appreciated.
Is nepheline syenite a variable ingredient? Thnaks for your help.
Oregon Rain (aka Floating Blue) Cone 5
nepheline syenite 50.25
silica 20.25
frit 3134 12.00
cadycal 11.00
epk 5.00
whiting 1.50
Totals: 100.00 %
Also add:
red iron oxide 2.00
cobalt carbonate 1.00
rutile 4.00
bentonite 2.00
Unity Formula for OREGON RAIN:
0.104 K2O 0.554 Al2O3 4.075 SiO2
0.413 Na2O 0.488 B2O3 7.4:1 Si:Al Ratio
0.475 CaO
0.008 MgO
Percentage Analysis:
61.57 % SiO2
14.22 % Al2O3
8.53 % B2O3
2.47 % K2O
6.44 % Na2O
6.69 % CaO
0.08 % MgO
Vikki and Libby
Stilltree Pottery
on the beautiful McKenzie River in Oregon...
http://www.stilltreepottery.com
vikkid@earthlink.net
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