hal mc whinnie on wed 9 aug 00
ONLINE CERAMIC GLAZE COURSE LESSON SEVEN PART ONE
The floating blue glaze
Mary's blue glaze was in essence a cone 6 glaze fired to cone 8. It produced
the running blue effects that occur when rutile, copper, and bone ash are
added to the glaze.
When one add wood ash to the glaze the results become quite varied, some are
wonderful but others are highly problematical. The problem with ash glazes
is that the contents change as the different batches of ash are employed.
If one want stability make up a vast supply of wood ash, say enough for 5
years and mix it well.
The floating blue glaze because of its great appeal to the general public is
one glaze problem to try to master or at least understand.
Base glaze
Illuminate 2
Neph syneite 40
Flint 25
Mag carb 3
Zinc oxide 5
Colemanite 7
Whiting 10
Bone ash 4
Rutile 3
We have tested the above glaze at both cone 8-10 reduction and cone 6
oxidation and it seems to do well in both kilns. If fired to cone 6 be sure
that cone 6 is absolutely flat. When fired to cone 8 expect the glaze to run
so protect the kiln shelves.
We have tested the glaze both with and without wood ash with good results.
For color
Runny green 10 g of copper oxide
Runny tan 10 g of nickle oxide
Runny yellow 10 g of vanadium or pentoxide
Runny red 10 g of crotus matous
And for runny blue
5 g cobalt carbonate
Ann's blue for salt
Custer spar 89
Whiting 10
Rutile 3
Iron 2
Soft blue in salt
Remember that the salt process is almost a glaze in itself.
BLUE SELLS
Hank Murrow on wed 9 aug 00
Hal McWhinnie wrote:
When one add wood ash to the glaze the results become quite varied, some are
>wonderful but others are highly problematical. The problem with ash glazes
>is that the contents change as the different batches of ash are employed.
>If one want stability make up a vast supply of wood ash, say enough for 5
>years and mix it well.
And Hank responds: I agree that glazes containing vegetable ashes will
vary, and agree that large reserves are a good idea. BUT, an unremarked
problem with these ashes, is that the solubles are being taken(along with
the water) at a greater rate than the solids when glazing. Thus, the actual
'recipe' will change from one glazing session to the next. I suppose one
could figure out some test for the soluble portion and adjust by adding
more ash each time until the batch is returned to its original proportions;
but I don't have the necessary knowledge. maybe a chemist among us could
devise a simple quantitative test. All we need is a relative measure of the
soluble stuff to compare and adjust to. Hank in Eugene
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