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ways to encourage"micro-crystalline growth in low-fire

updated tue 30 sep 03


George Koller on mon 29 sep 03

Hi Again Gang,=20

Thank you Ivor, and thank you Tom Buck for info/advice.

When we dispense "higher" concentrations of Iron to our Cone 04=20
zinc oxide opacified base white glaze we start to see what I now
think is "micro-crystalline" growth. (One day we had never seen
this before, the next day we "need it". We are hooked, whatever
this is we are seeing.)

...What we see is a "maze" of light green "lines" usually about
1/4" long and often at right angles to each other. White gaps b
etween. Rather subtle - not big radiating "classical" crystals at=20
all. And this is what we want.

What I'd like to do is compile a list of things we can do without
starting a major research project to encourage this to happen. =20

Here is what I have picked up so far:

1. Zinc oxide is a good media

2. Higher concentrations of metal colorants (Iron, Copper, =
Cobolt...) may help

3. Cooling cycle is most critical.... lots of advice.... but look =
to slow down
cooling starting at something like 100d F below melting point.

4. Thicker glaze coating is better. (from FA's site)

5. Titanium dioxide might encourage crystal growth (not sure at =
about at cone 04)
6. Not sure yet but Laguna and BigCeramicStore seem to have =
standard glaze bases
that are designed to support crystal growth - maybe Macro and =

7. I added some Pottasium DiChromate to several test tiles and this =
changed the
crystal shape as well as changed the color to a darker green. =
I am encouraged to=20
experiment with just a percent or two of Copper also to our Fe =
(which is now=20
being dispensed as a Ferric Ammonium Citrate solution at 45g / =

8. What we are seeing may be called Aventurines. See =
Parmalee/Harman for more
information / review.

9. (Boosting the red iron oxide content of a reliable Tenmoku style =
up to 15 % or more can get you some very nice Blue Haematite =
.....gk note: probably na to low temp?)

10. Tony Hanson's site has an eBook version of the book: "Crystal =
Glazes: Understanding the process
and materials" by Fara Shimbo. However, when I down loaded =
it (?) it was only 10 pages - mostly
an intro and the index. Not sure what happened but eBook =
concept strikes me as a really good one -=20
you are getting a "subscription" to future updates - not just =
a static book. (Ahhh those cutting=20
edge Canadians.)
This is where I am right now except for some additional too vaque for me =
to put into words info from
the archives ie maybe 4 years ago a good clayart thread on this with a =
Ron Roy response or two) =20

Will appreciate additional advise.

Note: We are looking to keep this all at cone 04 for now. We are =
looking to do this on
a regular and predictable basis.

Many thanks for assistance,

george koller
sturgeon bay, wi - door county
northport, mi - leelanau county

two great places separated by 100 miles of great lake.