Dupre Mr Marcy M on wed 10 jul 02
Dear Glaze Sensei,
A few weeks ago, I mixed up a batch of Crackle White raku, and a batch of
Dolphin Blue raku. Did a raku fire and both glazes worked wonderfully. Had
about half a small bucket load of each left over, so I sealed the buckets
tightly and saved it.
This past weekend, I fired another raku, partly for some new work and
testing a Soldner Ghost stain, and partly for a demonstration for the
neighbors. I was embarrassed when the Crackle White didn't crackle and
wasn't white, but lumped in globules and turned a dingy yellow. The Dolphin
Blue turned black and copper and, in some cases, peeled and flaked off.
Is there such a thing as glaze ingredients going bad? Is there an
equivalent of a "Sell by" date for materials like Gillespie Borate? Does
Cornwall Stone go bad? (How can I tell?) Should I mix all glazes in fresh
batches for each fire?
Crackle White
Gerstley borate 70%
Cornwall Stone 15%
Tin oxide 10%
Flint 5%
Clement Dolphin Blue (from Piepenburg's book on raku)
Gerstley borate 7
Bone ash 3
Nepheline syenite 2
Cornwall Stone 1
Copper carbonate 1
Cobalt oxide 0.75
I substituted Gillespie Borate for Gerstley Borate. I've done it in the
past and have had no problems. Other materials were used as called for in
the recipe.
Enquiring minds NEED to know...
Thanks for any and all help,
Tig
in Springfield, VA where we had a badly needed and very refreshing rain last
night
Earl Brunner on wed 10 jul 02
Some materials are more soluble than others, once you have mixed water with them,
they can change the percentage of the material that is dissolved into the water
over time. I suspect that it's not so much that the materials have gone bad, (all
of the different chemicals are still there), it just that they act differently when
dissolved into the water. Some of the chemicals move with the water, into the clay
when the glaze is applied and don't remain on the surface with the rest of the
glaze. The glaze then as it begins to react to the heat of the firing doesn't have
those soluble materials in it to react to and with. The chemicals are elsewhere in
the pot.
Dupre Mr Marcy M wrote:
> Dear Glaze Sensei,
>
> A few weeks ago, I mixed up a batch of Crackle White raku, and a batch of
> Dolphin Blue raku. Did a raku fire and both glazes worked wonderfully. Had
> about half a small bucket load of each left over, so I sealed the buckets
> tightly and saved it.
>
> This past weekend, I fired another raku, partly for some new work and
> testing a Soldner Ghost stain, and partly for a demonstration for the
> neighbors. I was embarrassed when the Crackle White didn't crackle and
> wasn't white, but lumped in globules and turned a dingy yellow. The Dolphin
> Blue turned black and copper and, in some cases, peeled and flaked off.
>
> Is there such a thing as glaze ingredients going bad? --
Earl Brunner
http://coyote.accessnv.com/bruec
mailto:bruec@anv.net
Julie Milazzo on wed 10 jul 02
--- Dupre Mr Marcy M
wrote:
Did a raku fire and both glazes
> worked wonderfully. Had
> about half a small bucket load of each left over, so
> I sealed the buckets
> tightly and saved it.
>
> This past weekend, I fired another raku. I was
embarrassed when the Crackle White
> didn't crackle and
> wasn't white, but lumped in globules and turned a
> dingy yellow. The Dolphin
> Blue turned black and copper and, in some cases,
> peeled and flaked off.
>
> Is there such a thing as glaze ingredients going
> bad? Is there an
> equivalent of a "Sell by" date for materials like
> Gillespie Borate? Does
> Cornwall Stone go bad? (How can I tell?) Should I
> mix all glazes in fresh
> batches for each fire?
>
I know that bone ash can get fairly nasty, but have no
idea about a shelf life for any of these ingredients.
I will suggest, however, the method that my former
teacher Marv Bjurlin at fredonia State uses for his
raku glazes. He dry mixes all the ingredients in a big
batch, and stores them in lidded containers, dry.
Then, when it's time to glaze, a little of the mix is
put into a yogurt container, and water is added. There
is usually very little left over, and I always figured
that there must be a reason why they weren't stored
wet like the reduction glazes. Hmmm.... how
disappointing for you. Just when you think you've got
a handle on things...
Julie, on lovely St. Helena Island, where the cicadas
are chirping, the kittens are playing, and the
tortoises are doing little, as usual... as am I
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Cindi Anderson on wed 10 jul 02
This can happen to Raku glazes, I believe it is because of the gerstley
borate. I have often heard that Raku glazes like to be mixed up fresh.
Cindi
----- Original Message -----
From: "Dupre Mr Marcy M"
> A few weeks ago, I mixed up a batch of Crackle White raku... This past
weekend, I fired another raku...I was embarrassed when the Crackle White
didn't crackle and wasn't white, but lumped in globules and turned a dingy
yellow
Snail Scott on wed 10 jul 02
At 11:55 AM 7/10/02 -0700, you wrote:
I was embarrassed when the Crackle White
>didn't crackle and wasn't white...Gillespie
>Borate...
I don't know what's in Gillespie Borate, but
many borax-type materials are soluble. The
recipe is probably proprietary, but the
manufacturer might at least tell you the
solubility of the stuff if you ask. If it's
a recipe that works otherwise, just mix up
a big dry batch, and only wet the amount
needed for each glazing session.
The waste can be minimized by glazing large
quantities of work occasionally, instead of
just a few at a time more often. Also, pouring
and brushing require less excess glaze than
dipping. Even if you dip most of your work,
you can use up the last of a batch with these
other methods and have less waste.
-Snail
Jeff Tsai on wed 10 jul 02
Tig,
This sounds really weird...maybe someone is out to get you and sabatoged your
glazes.
I know it's asking you to do more work, but I'd be interesting in hearing the
results if you did a couple tests. make a couple test pieces and use both
glazes again and fire them and tell us the results...
At the same time, mix a very small batch of both glazes again and test
them...let them sit for a couple weeks and test them again.
Maybe it was just a fluke...
You white crackle glaze is very similar to the one we use at our school, and
our glazes sit for weeks at a time without use, sometimes an entire summer
goes by without use.
I'd like to know the results, but it's up to you cause it's work for ya.
-jeff
Peter Coates on wed 10 jul 02
i have had raku glazes sit for over a year (containing gerstley borate) and
allways fire fine... from what you have discribed i would think that the
glazes were underfired.
pete in OKC, OK
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