iandol on mon 25 mar 02
Dear Lee Love
You say <original Chun glazes. It can be introduced from ashes or bone ash. P2O5 =
opacifies by suspending small gas bubbles in the glaze. These bubbles =
act like a prism giving the same type of blue in the glaze you see in =
the blue sky.>>
Perhaps you could explain the chemistry which produces gas from =
Phosphorus Pentoxide. What gas is it and what are the other chemical =
which are reacting with the P2O5?
It has always been my understanding that phosphorus pentoxide, derived =
mainly from calcium phosphate derived from bones or plant ash is a glass =
former. Because a phosphoric glass melt does not mix with a silicate =
glass melt it tends to ball up and dispersed through the silicate mass =
in a the manner of a colloid. I understand the blue colour is seen =
because light wavelengths in the Orange spectral range are adsorbed =
whereas wavelengths in the blue region are reflected. If you could look =
outwards at the glaze from the surface of the pot you would see brown.
Best regards,
Ivor Lewis
vince pitelka on wed 27 mar 02
Ivor -
I am under the impression that the irridescence and color of true Chun
glazes are due to microscopic globules of phosphorus suspended in the glaze
melt? Isn't it the reflective qualities of those small spheres of
phosphorus, rather than gas bubbles?
Best wishes -
- Vince
Vince Pitelka
Appalachian Center for Crafts
Tennessee Technological University
1560 Craft Center Drive, Smithville TN 37166
Home - vpitelka@dtccom.net
615/597-5376
Work - wpitelka@tntech.edu
615/597-6801 ext. 111, fax 615/597-6803
http://www.craftcenter.tntech.edu/
iandol on wed 27 mar 02
Dear Lee Love,
Well, a pretty crude way of putting it, but I suppose it will depend on =
the source of your "Bone Ash". I presume you have an analysis? I suppose =
you tested for methane?
I would suggest that the bubbles come from reduction by residual carbon =
which tends to contaminate many animal bye-products. They just increase =
the opacity. Blue still comes from adsorption of longer wave lengths and =
reflection of the shorter.
Best regards,
Ivor.
Lee Love on wed 27 mar 02
----- Original Message -----
From: "iandol"
>Perhaps you could explain the chemistry which produces gas from Phosphorus
>Pentoxide. What gas is it and what are the other chemical which are reacting
>with the P2O5?
Hi Ivor. I used a electron microscope to examine the action at around 2300*F
and I saw little gremlins in the glaze, emitting farts from their anuses. ;^)
Seriously Ivor, I don't know, but you can do the same experiment as I
did and mix up my Chun recipe with and without bone ash. Without the bone
ash, you don't have bubbles. I'll share the recipe later (just home for lunch.
http://www.matrix2000.co.nz/GlazeTeach/Unit_6/Topic_6_12.htm
Phosphorous Pentoxide - P2O5
Amphoteric Unit 6 Topic 12
Oxide Qualities
Colloidal blues - opacifies with suspended small gas bubbles - sourced from ash.
.
Action
Although technically an amphoteric P2O5 acts more as a glass-forming oxide
though not a substitute for silica.
Present as a trace element in some materials.
Small amounts give colloidal opacity e.g. chun glazes.
Creates a matrix of small bubbles in a glaze giving light dispersal particularly
pleasant in celedons.
Shows as a bluish flush in a glaze.
Large amounts give opacity, dull surface and blistering.
http://www.matrix2000.co.nz/GlazeTeach/Unit_6/Topic_6_12.htm
--
Lee In Mashiko, Japan Ikiru@kami.com
"We can only wait here, where we are in the world, obedient to its processes,
patient in its taking away, faithful to its returns. And as much as we may
know, and all that we deserve of earthly paradise will come to us."
Wendell Berry , Full Quote: http://www1.ocn.ne.jp/~ikiru/berry.html
Hank Murrow on thu 28 mar 02
Vince wrote;
>Ivor -
>I am under the impression that the irridescence and color of true Chun
>glazes are due to microscopic globules of phosphorus suspended in the glaze
>melt? Isn't it the reflective qualities of those small spheres of
>phosphorus, rather than gas bubbles?
>
Dear Vince and Ivor;
Actually, the globules are a phosphoric glass suspended
within the silicate glass. Phosphorus is a glass-former like silica,
but useful at higher temperatures. One of my glazes is 50% bone ash,
and lovely! Currently, I am trying to get some microscopic pics taken
of cross-sections of such glazes, which when acid-etched, will show
the phosphoric globules floating in the silicate glaze.
Best, Hank
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