Zoe Paddy Johnson on wed 9 jul 03
I have finished grinding up my granite and have ended up with about a pint
of granite jello :-). It has been suggested that I add and equal volume of
ash. Is this by weight or volume?
Last weekend, one of my "tame geologists" (my son) and I went glaze
ingredient hunting. We came up with some really old red and black granite
(1.85+By), some volcanic ash, some obsidian, some sandstone that has been
mined in the past as a copper ore, and a lot of beer bottles. I am going
to "calcine" one of these before I toss it in the rock tumbler. I was
going to pound on it (probably the obsidian) with a crack hammer and safety
glasses, throw a small vertically oriented something , fill it with debris,
and bisque the debris to 06. Does this sound okay?
ZoeJ
Hank Murrow on wed 9 jul 03
On Wednesday, July 9, 2003, at 10:56 AM, Zoe Paddy Johnson wrote:
We came up with some really old red and black granite
> (1.85+By), some volcanic ash, some obsidian, some sandstone that has
> been
> mined in the past as a copper ore, and a lot of beer bottles. I am
> going
> to "calcine" one of these before I toss it in the rock tumbler.
Dear Zoe; I think you do not need to calcine the beer bottles as they
have no water of crystallization in them. The reason for calcining
granite is to drive off the water of crystallization in the feldspar.
This makes it easier to hammer down to 'grog' size, before grinding up
in a ball mill. The beer bottles will likely puddle on your kiln
shelves.
To summarize, place all the granite chunks or other naturally occurring
minerals in a bisque bowl and fire to 06, then crush with a hammer and
ball mill from there.
Cheers, Hank in Eugene
iandol on thu 10 jul 03
Dear Hank Murrow,
"Water of Crystallisation" in Felspar, in M2O-Al203-6SiO2. ?
This is a differential thermal expansion thing. I think it may be =
Anisotropic in the felspars and the mica, with Phase Change in the =
quartz which causes the breakdown
Best regards,
Ivor Lewis
Steve Harrison on thu 10 jul 03
Dear Hank
With all due respect. I don't think that we calcine granite to remove water of crystalisation.
Granite doesn't have any. Typically less than 1%.
As I understand it, granite is calcined because it has quartz crystals which expand unevenly,
quartz has a sudden alpha/beta phase change at 573 degrees centigrade. The other two
crystals involved, mica and felspar don't have this property. This uneven expansion and
contraction causes all the crystals to separate, hence the rock is easier to crush after
calcining. The temperature only needs to exceed 573 at the heart of the lump of rock. For
lumps up to 6" to 8" 800 degrees centigrade will be OK.
regards
Steve
John Britt on thu 10 jul 03
Another thing that I have noticed is that after heating the granite if it
doesn't crunble immediately just wait a day or so and it will then crumble
into a pile of its own accord.
Hope you have fun,
John Britt
steve harrison on thu 10 jul 03
on 10/7/03 3:56 am, Zoe Paddy Johnson at pjohnso@UNM.EDU wrote:
Dear Zoe
You will find your job of primary crushing a lot easier if you calcine the
big chunks first before you do anything at all to them. Then they will break
up a lot easier. This will work very well on everything except the obsidian,
which being glass doesn't have any crystals boundries to shatter along.
Please don't just add ash indiscriminately. You've gone to some trouble to
grind it all up. Take a systematic approach, it doesn't take long to do a
line blend and you'll get the best possible answer for your rock.
If I may be a little forward in pushing my book
"Rock glazes and mineral processing for potters"
it may be of interest to you.
http://ian.currie.to/sh/Steve_Harrisons_books.html
best wishes
Steve harrison
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