George Koller on fri 26 sep 03
Attention Glaze Gurus,=20
We are dispensing the metal salts onto a nominally white
base glaze for decoration. My question involves a Iron
salt saturated into a cone 04 glaze that uses zinc oxide=20
as a whitener.
Fairly recently we started using the "fast ramp" or about
3.3 hour cycle to cone 04 rather than the "medium ramp"
or about 6 hours because we really like the more interesting=20
texture it gives to the glaze. =20
I should also note that we are just getting ready to process
some pretty big orders ( for us ) so I've been working to=20
gain more consistency and a better understanding of all
of our (many many) process variables. Overall things have=20
been going along pretty much as one might expect with all=20
of this - until just yesterday.
Yesterday, when the kiln was at about 800d F I raised
the kiln lid to take a peek or two.
I can't be entirely certain if it was related to those peeks
but this batch of test tiles seemed to have a much more
pronounced "crystal" pattern than any previous. =20
Today I did an experiment back at medium ramp with a
30 minute hold at the end temp and the glaze came out=20
entirely without any texture - and looking boring -=20
one might even say "sickly" after spending some time
studying that "crystaline" texture. =20
Here are some of my questions:
1. Is "Crystalinity" most likely to be what we are seeing?
=20
2. Are there perhaps other phenomena / terms that might
apply?
3. Where / how can I learn more about Iron and crystaline
glaze effects?
4. Is the cooling cycle critical to crystal formations and=20
if so what can / should I begin looking at to gain better
control over the critical parameters?
=20
Clues and comments will be appreciated. If I get into this it
will have been by accident, but a good one. Right now I feel
like more variables are the last thing in the world we need but
the glaze with crystals just seem so much more "alive". =20
Thanks,
George Koller
In Northport, MI on a cool rainy fall day. A great "bakery day" which
is just darned nice because Northport just happens to have the greatest=20
little bakery in the world. The leaves here must have been frosted=20
recently because the first hints of red is showing up.... oh oh... the =
city
folks will be coming up soon enuf to see'em.
iandol on sat 27 sep 03
Dear George Koller,
You say <lid to take a peek or two.>>
At that kiln temperature the interior of your tiles would have been at a =
higher temperature, probably in the danger range for Quartz phase =
transformation. Chilling might have initiated a destructive response. I =
suggest you examine your "Crystalline" surface with a high power lens =
and do some sort of dye disclosure test to see if your glazes have =
crazed.
Yes, Cooling Rates are critical in the development of true crystalline =
glazes. In the case of Zinc Crystal glazes it is common practice to =
arrest the decline in temperature for a period of time. The best actual =
temperature is determined in the usual, test, test, test. Lot of =
information in the archives about the books. Have a look in Ceramics =
Technical, no 13, 2001. p 8. "Predicting Glaze Phase Transformations".
To get good Iron glaze, look for "Saturated Iron Glaze" recipes. =
Boosting the red iron oxide content of a reliable Tenmoku style recipe =
up to 15 % or more can get you some very nice Blue Haematite crystals.
Best regards,
Ivor Lewis. Redhill, South Australia=20
Ron Roy on mon 29 sep 03
Hi George,
I have no experience at cone 04 but I am pretty sure we are still talking
about the same thing.
Levels of iron are important - start at 10% and do a series, 11, 12, 13, 14
and 15 % - each glaze will have a slightly different amout of iron it can
hold in suspension - and much depends on the cooling cycle. Cool fast
enough and you can eliminate crystal formation entirely.
We cover this aspect in our book by the way.
The higher the iron level the faster you can cool and get the surface you want.
Most books say not to use a zinc glaze with iron because you get muddy
browns - don't know if this applies to crystalline iron on the surface.
RR
We cover this aspect in your book by the way.
>Here are some of my questions:
>
> 1. Is "Crystalinity" most likely to be what we are seeing?
>
> 2. Are there perhaps other phenomena / terms that might
> apply?
>
> 3. Where / how can I learn more about Iron and crystaline
> glaze effects?
>
> 4. Is the cooling cycle critical to crystal formations and
> if so what can / should I begin looking at to gain better
> control over the critical parameters?
>Clues and comments will be appreciated. If I get into this it
>will have been by accident, but a good one. Right now I feel
>like more variables are the last thing in the world we need but
>the glaze with crystals just seem so much more "alive".
>George Koller
Ron Roy
RR#4
15084 Little Lake Road
Brighton, Ontario
Canada
K0K 1H0
Phone: 613-475-9544
Fax: 613-475-3513
Ababi on mon 29 sep 03
Most books say not to use a zinc glaze with iron because you get muddy
browns - don't know if this applies to crystalline iron on the surface.
RR
================= original ababi ======================
You are right Ron.
If I ever write a book I shall write: Do not have it as a fact that Zinc
and Iron should not be together.
And I would add at least three recipes.
Ababi
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