Michael Banks on sat 27 nov 99
------------------
Finally, some reliable observations on the petuntse rock in Hank Murrows
informative post yesterday. So it's an aplite dyke, great, now we're getting
somewhere.
I knew it couldn't be an altered rhyolite (as suggested by someone
previously), as the feldspars in these volcanic rocks are usually fatally
contaminated with too much iron and titanium to make porcelain. Aplites are
sugary-textured dyke rocks found associated with granite and are intrusive.
They are (usually very low iron and titanium) mixtures of quartz, feldspar
and a variety of other minerals including micas, fluorite, topaz etc. The
=22clay-sized muscovite=22 content raises a question though. If is really
=22clay-sized=22 mica? If it is truly micron to sub-micron (colloidal) in =
size,
then this stuff may in fact be plastic illite.
Illite is virtually identical, chemically and structurally to muscovite but
is a true clay mineral, compared to muscovite which is a mica. Illite is a
alteration product of neutral pH hot waters acting on feldspars, whereas
muscovite (much more crystalline) is a product of higher
temperature/pressure regimes. If the hot waters are acidic, kaolin clay
results (as in the well-known Cornish china clay deposits).
Petuntse has often been likened to English Cornish stone, but Cornish stone
is non-plastic and fairly refractory (being rich in kaolin). If petuntse
has a significant (=7E20=25) illite component, it would be white, plastic =
AND
low-ish firing. These qualities are very special and would have assisted
the great technological breakthrough that the invention of Chinese porcelain
was. Just a bit of SCIENCE here (with apologies to Elizabeth Priddy)...
Michael
in NZ
Hank Murrow wrote: (snip)
I include some remarks from David Stannard, who visited these Petuntse mines
for your information here: =22I can't remember, either, responding to your
query about Jingdezhen quarry-- Did I reveal my ignorance on that one
already?? I have only speculation following on the visit I made to the
quarry entrance back in '82. It's very
near a small stream, =26 now goes down underground at a steep angle on =
rails,
7 km in an arc following down the dyke of altered Aplite(spar,qtz , =3C20=25
clay-sized muscovite and =3C1=25 siderite, FeCo3, as I recall). Where it =
comes
out to
the next valley is an area where they get kaolin to add to the pulverized
P-stone for a body(adding, also, I believe, some montmorillonite for
plasticity). From the topography =40 mine-entrance I speculate, for myself,
that the altered
Aplite exposed at creek bank in early days weathered out to a plastic,
Fe/Ti-free clay that, as they used it up in production, they followed down
underground =26 began having to mill it to release the clay-mica when =
passing
beyond the weathered zone. Pure speculation, but consistent with head/hands
pragmatic approach to 'follow your nose' potter's proclivities. Any scenario
more complicated I would discount as intellectual's daydream. As
clay-muscovite fraction diminished they'd benefit by adding kaolin =26
'bentonite'(montmorillon- itic) clays to keep it workable. The 60m dyke has
been followed for 1000yrs, =26 I don't know whether they've picked-up on =
other
regional sites, as that could class as 'trade-secret'. Currently, they do
add kaolin. Pamela Vandiver will surely know more about that sort of
historical shift, but if she doesn't, I know a guy =40 Shanghai Inst. of
Ceram. I could write to, if you
are really interested. Also, Tichane may have a good idea, tho I think he
pulled out of Ceramic interests a while back. I don''t know where the kao
ling name came from, tho seems I did read a ref. to hills named such. Agin,
I'm to careless a person to know those things.=22 David has been
pioneering the prospecting of natural porcelain-stones along the Pacific
Rim, from California through Oregon and Washington to Alaska, where he now
resides. What he found was that the Rhyolites(Fe/Ti-free volcanics) often
contained large fractions of the mineral Sericite, a plastic micaceous form
leading to a useful natural porcelain. A deposit many may be familiar with,
is located in the Mohave desert in CA, and is sold as Plastic Vitrox. Others
have more or less alkali content, depending upon subsequent hydrothermal
alteration and weathering processes. I mine and process such a Rhyolite
which has had about half the alkalis removed by alteration and some FE and
Ti came along with the steam and hot water to render this porcelain-stone
not translucent in C/10 fires, but beautiful shades of tan to mahogany brown
with a slightly self-glazed surface from remaining solubles=3B to =
irridescent
black in the anagama firing. It is called Calf Ridge Porcelain-stone.
Interestingly, if one adds 15-20=25 limestone to this body=3B the result is =
a
lovely greenish (due to the Ti) celadon which has a phenomenal fit to its
body, ringing like a bell. This is the way those early Chinese potters did
the gorgeous Sung
wares. They found clean extrusive (volcanic) rocks and ground them up for a
body, added lime to it for a glaze, and voil=E0, celadon=21 I have in my
collection several bowls made by David from Porcelain-stones gathered all
along the Pacific coast, which are self-glazed(added Limestone) celadons
all, and translucent. In fact, they are translucent at C/8, where they
exhibit that muttonfat quality you mention. If there's any significant Ti
present, they will not be translucent, and will be green not bluish in
color. So Jon, I suggest you make friends with a geologist or
well-driller(or both) to locate some hydrothermally altered and weathered
Rhyolite to try. Should be some in your islands due to their volcanic
nature. And if you fire your samples in a large multi-chambered kiln (as
the Sung potters did), stack them in the first two chambers where they will
cool relatively quickly while the subsequent chambers are still beingstoked.
By the time the last chamber was finished abd the firebox was sealed, those
first two were nearly dark. Or just fire them in a little (27cuft) kiln as I
do. Wish I could show you some pics. Good Luck=21 Hank in
Eugene
Hank Murrow on wed 1 dec 99
>----------------------------Original message----------------------------
>Finally, some reliable observations on the petuntse rock in Hank Murrows
>informative post yesterday. So it's an aplite dyke, great, now we're getting
>somewhere.
>
>I knew it couldn't be an altered rhyolite (as suggested by someone
>previously), as the feldspars in these volcanic rocks are usually fatally
>contaminated with too much iron and titanium to make porcelain. Aplites are
>sugary-textured dyke rocks found associated with granite and are intrusive.
Snip: From Cardew, page 7, "Of particular interest to potters is the
special class known as 'differentiated' hypabyssal rocks, so called because
they arose from a separation or 'differentiation' of the parent magma into
two liquids of different composition, the one more acid, the other more
basic. They are sometimes called 'leucocratic' and 'melanocratic' because
the first tends to be white, the second, black. The acid group includes the
well-known pegmatites and aplites, which are almost free from iron
minerals."
The point I wish to make in regard to Petuntse is that it is a
better path to quit moaning about the absence of good kaolins in your
neighborhood, when one might inquire about local volcanos and the rhyolites
and aplites which they may have generated. The fact is, they carry the
alkaline fluxes AT THE MOLECULAR LEVEL within the clay lattice. This is
what makes possible a natural, sometimes translucent(if there's not much
Ti) porcelain-stone @ C/8+. The only reason the Japanese and the Europeans
settled on Kaolin was that they found that first, and mistakenly thought
they had the Secret of Porcelain. Hank
snip;
>Petuntse has often been likened to English Cornish stone, but Cornish stone
>is non-plastic and fairly refractory (being rich in kaolin). If petuntse
>has a significant (~20%) illite component, it would be white, plastic AND
>low-ish firing. These qualities are very special and would have assisted
>the great technological breakthrough that the invention of Chinese porcelain
>was. Michael in NZ
These are exactly the qualities of Petuntse which David Stannard
has experienced at their mines and in his own studio with samples brought
back from Jingdezhen. He has had electron microscopy and mineral analysis
done on these chinese samples along with those he has collected from
California to Alaska, arriving at the conclusion that sericitic quartz
rocks, whether originating from altered rhyolites or aplite dykes were most
like the Petuntse used by the sung potters. They range from white to
stoneware in hue, and mature @ C/8-9. I have a little collection of bowls
made by David, which has been the inspiration for my porcelain-stone
gathering during the last three years. You can count your fingers through
most of them when held up to the light. Hank in Eugene
Khaimraj Seepersad on thu 2 dec 99
Anyone ,
A question , where do you fit a micaceous clay ,
which fires just off white at 1230 deg.c and is
translucent when thin .
The area the material comes from is 3 feet below
the surface , and depositional .We have no
volcanicity . Supposed to form
In Situ , and is sometimes plastic , but very plastic
with 1 to 2 bentonite .
Also shiny , slippery and sticky .
Chemically [ variable ] has -
75 to 65 % Si02
17 to 22.5 % Al203
a 10 % LOI
and less than 1% Fe203 [ ? ]
less than 1% K20 / Na20
some Ca0 and Mg0
The deposits are too small commercially but would
keep many potters happy .
Forms a translucent body with 30 to 40 % Nepheline
Syenite at 1180 deg.c
I am curious -
Khaimraj Seepersad
-----Original Message-----
From: Hank Murrow
To: CLAYART@LSV.UKY.EDU
Date: 01 December 1999 12:19
Subject: Re: Petuntse/Celadons
----------------------------Original message----------------------------
>----------------------------Original message----------------------------
>Finally, some reliable observations on the petuntse rock in Hank Murrows
>informative post yesterday. So it's an aplite dyke, great, now we're
getting
>somewhere.
>
>I knew it couldn't be an altered rhyolite (as suggested by someone
>previously), as the feldspars in these volcanic rocks are usually fatally
>contaminated with too much iron and titanium to make porcelain. Aplites
are
>sugary-textured dyke rocks found associated with granite and are intrusive.
Snip: From Cardew, page 7, "Of particular interest to potters is the
special class known as 'differentiated' hypabyssal rocks, so called because
they arose from a separation or 'differentiation' of the parent magma into
two liquids of different composition, the one more acid, the other more
basic. They are sometimes called 'leucocratic' and 'melanocratic' because
the first tends to be white, the second, black. The acid group includes the
well-known pegmatites and aplites, which are almost free from iron
minerals."
The point I wish to make in regard to Petuntse is that it is a
better path to quit moaning about the absence of good kaolins in your
neighborhood, when one might inquire about local volcanos and the rhyolites
and aplites which they may have generated. The fact is, they carry the
alkaline fluxes AT THE MOLECULAR LEVEL within the clay lattice. This is
what makes possible a natural, sometimes translucent(if there's not much
Ti) porcelain-stone @ C/8+. The only reason the Japanese and the Europeans
settled on Kaolin was that they found that first, and mistakenly thought
they had the Secret of Porcelain. Hank
snip;
>Petuntse has often been likened to English Cornish stone, but Cornish stone
>is non-plastic and fairly refractory (being rich in kaolin). If petuntse
>has a significant (~20%) illite component, it would be white, plastic AND
>low-ish firing. These qualities are very special and would have assisted
>the great technological breakthrough that the invention of Chinese
porcelain
>was. Michael in NZ
These are exactly the qualities of Petuntse which David Stannard
has experienced at their mines and in his own studio with samples brought
back from Jingdezhen. He has had electron microscopy and mineral analysis
done on these chinese samples along with those he has collected from
California to Alaska, arriving at the conclusion that sericitic quartz
rocks, whether originating from altered rhyolites or aplite dykes were most
like the Petuntse used by the sung potters. They range from white to
stoneware in hue, and mature @ C/8-9. I have a little collection of bowls
made by David, which has been the inspiration for my porcelain-stone
gathering during the last three years. You can count your fingers through
most of them when held up to the light. Hank in Eugene
Michael Banks on fri 3 dec 99
Looks like an impure kaolin from the limited data, Khaimraj.
Silica (quartz) is the main impurity from the analysis, being possible as
high as one third. Less than 10% mica present -judging by the low K2O
content. The relatively low maturity point (1230oC) you quote is
interesting and along with the semi-plasticity, suggests that it has a
significant plastic, colloidal (i.e: ballclay type) component.
You could try separating the plastic component from the diluting quartz, by
settling (levigating) with Calgon or another dispersant. Siphon off the top
suspended layer (as in making terra sigillata), flocculate the decanted slip
with acid or Epsom salts, leave to settle (might take days, weeks?), siphon
off the clear water and de-water the concentrated slip in plaster
molds/batts. You might end up with a nice ball clay, but it may not fire as
white as the less plastic original. Still, you may be able to use it
instead of bentonite to make the original clay throwable....
I assume tt (in your email adress) is somewhere warm... Moderately
white-firing, semi-plastic kaolin type clays are common in the wet tropics
as part of the laterite profile (pallid zone). They form in-situ from the
strong cation leaching effect (on any bedrock containing some feldspar) of
the naturally acid ground waters in tropical climates. The extreme end-point
of this type of weathering, if carried to completion, is removal of
virtually all the alkalis and silica, making bauxite (alumina ore).
Michael,
in NZ
> ----------------------------Original message----------------------------
> Anyone ,
> A question , where do you fit a micaceous clay ,
> which fires just off white at 1230 deg.c and is
> translucent when thin .
>
> The area the material comes from is 3 feet below
> the surface , and depositional .We have no
> volcanicity . Supposed to form
> In Situ , and is sometimes plastic , but very plastic
> with 1 to 2 bentonite .
> Also shiny , slippery and sticky .
>
> Chemically [ variable ] has -
> 75 to 65 % Si02
> 17 to 22.5 % Al203
> a 10 % LOI
> and less than 1% Fe203 [ ? ]
> less than 1% K20 / Na20
> some Ca0 and Mg0
>
> The deposits are too small commercially but would
> keep many potters happy .
> Forms a translucent body with 30 to 40 % Nepheline
> Syenite at 1180 deg.c
>
> I am curious -
> Khaimraj Seepersad
Michael Banks on sat 4 dec 99
Hank Morrow wrote: "The point I wish to make in regard to Petuntse is that
it is a
>better path to quit moaning about the absence of good kaolins in your
>neighborhood, when one might inquire about local volcanos and the rhyolites
>and aplites which they may have generated. The fact is, they carry the
>alkaline fluxes AT THE MOLECULAR LEVEL within the clay lattice. This is
>what makes possible a natural, sometimes translucent(if there's not much
>Ti) porcelain-stone @ C/8+."
This is a good point, although you mistakenly associate volcanoes and
rhyolites (deposited in a volcanic environment), with aplites, which are a
purely intrusive (plutonic/hypabyssal) rock genetically and spatially
associated with granites.
My own experience has led to the conclusion that low iron & titanium (i.e:
white-firing and translucent producing) plastic clays, including built-in
fluxes, are exceedingly rare. The general problem is that the natural
processes that produce plastic clays, clean fluxes and low-Fe, Ti content,
are ALL antithetical. Virtually all porcelain and porcelain clay
manufacturers (past and present) have had to use kaolin, feldspar and silica
mixtures.
Petuntse was one of those happy geological gifts that gave mankind something
new. It underlines the importance of the raw material accessibility factor
in discovering new technology, - bronze was first made by people who had
plenty of copper and tin around to experiment with. Porcelain was
discovered by people who had petuntse to play with...
Petuntse was so exceptional that it proves the rule. The fact that David
Stannard has had to ransack virtually the entire western cordillera of North
America (one of the most mineral-rich parts of the entire planet), to come
up with a few petuntse-like rocks, is instructive. And though he found some
deposits, how many are big enough to be in production? But don't stop
searching for this holy grail on my account. I salute your perseverance.
If you find a significant workable deposit, gimme a chance to be in on the
ground floor, it will be a winner.
And Hank also wrote:
>"The only reason the Japanese and the Europeans
>settled on Kaolin was that they found that first, and mistakenly thought
>they had the Secret of Porcelain."
I have to say I think this is a wild generalisation Hank. There are other
factors involved here. IMHO the probable reason the Japanese and Europeans
stuck with kaolin was purely geological. Hydrothermally altered, low iron
rhyolites are rare or absent in Europe. As for Japan, I don't know, but
doubt that the pragmatic Japanese would ignore a plastic petuntse-type rock
if they had any. And anyway (as I mention above) WE STILL use kaolin base
clays almost exclusively to make porcelain -and it aint an accident.
Michael Banks,
Nelson
NZ
Khaimraj Seepersad on sun 5 dec 99
Good Afternoon , Michael ,
Just to say thank you , for the information . Yes , to all about the
tropical
wet zone .
The clay responds well to cleaning , using the Chinese technique , and
acetic acid settles the slip , very rapidly .
Altogether very easy to clean , I pass the slip through a -325 mesh and
after settling for 20 minutes , siphon off the floating clay for fine work .
Aside -
The British Museum Book of Art -
has many references to Huashi - slippery stone - a white-firing Kaolin with
with a fair content of white mica .
Added to
Porcelain stone
These wares are known as - Chinese
soft Paste
Porcelain .
The book also mentions Porcelain Stone as being mostly quartz ,and large
amounts of the plastic mineral
hydro - mica . Some
varieties having lesser amounts of
feldspars and/or
true clay minerals , mainly
kaolinite .
Those varieties richest in micas and clays could be made into porcelain
without further additions .
Those with lower plasticity and greater fusibilty were more usually mixed
with
kaolin .
That Southern Chinese kaolin is rich in a close relation of Kaolinite known
as
Halloysite .
That in Chinese Ceramics , Potassium Mica takes the place of Feldspar .
Also stating that Southern Chinese Porcelains are largely Micaceous ,
including
Longquan celadon bodies .
The term Petuntse is now Bai Dunzi , but the term for Porcelain Stone today
is
Cishi .
I am not sure just how plastic is plastic . As I have noted the Chinese
throwing ,
thickly and shaving down the object . Having used pressing , onto or into a
mould .
These people are practical to a fault . I could see them accepting the
"limitation "
or Porcelain Bodies and just working with it .
Ancient Egg Shell thinness seems to be happy kiln accidents , there are
reports
of mountains of wasters .
Happy to be educated otherwise .
Notes of Interest ,
Chinese Copper Red - a colloidal copper metal at 0.5 % Cu. [ prime source ]
Tio2 being responsible for the huge range of greens , in Chinese Celadon
Glazes .
This one I have observed - I used a simple Alkaline Glass - Na20,Li02 ,
Si02 ,
[ Al203 at less than or equal to 5.1 % ] , plus 1 to 8 % Tio2 and less than
1 % Fe203
Went from Watery Sky Blue to Green to Golden Green .
Another Battery of tests included less Al203 , and additions of 1 to 5 %
Alkalines ,
from Mg0 , Ca0 and Sr0 . Went through Greens to Golden Browns .
These tests were done as Glass .
Hope this adds to your research ,
Khaimraj Seepersad
>
>This is a good point, although you mistakenly associate volcanoes and
>rhyolites (deposited in a volcanic environment), with aplites, which are a
>purely intrusive (plutonic/hypabyssal) rock genetically and spatially
>associated with granites.
>
>My own experience has led to the conclusion that low iron & titanium (i.e:
>white-firing and translucent producing) plastic clays, including built-in
>fluxes, are exceedingly rare. The general problem is that the natural
>processes that produce plastic clays, clean fluxes and low-Fe, Ti content,
>are ALL antithetical. Virtually all porcelain and porcelain clay
>manufacturers (past and present) have had to use kaolin, feldspar and
silica
>mixtures.
>
>Petuntse was one of those happy geological gifts that gave mankind
something
>new. It underlines the importance of the raw material accessibility factor
>in discovering new technology, - bronze was first made by people who had
>plenty of copper and tin around to experiment with. Porcelain was
>discovered by people who had petuntse to play with...
>
>Petuntse was so exceptional that it proves the rule. The fact that David
>Stannard has had to ransack virtually the entire western cordillera of
North
>America (one of the most mineral-rich parts of the entire planet), to come
>up with a few petuntse-like rocks, is instructive. And though he found
some
>deposits, how many are big enough to be in production? But don't stop
>searching for this holy grail on my account. I salute your perseverance.
>If you find a significant workable deposit, gimme a chance to be in on the
>ground floor, it will be a winner.
>
>And Hank also wrote:
>
>>"The only reason the Japanese and the Europeans
>>settled on Kaolin was that they found that first, and mistakenly thought
>>they had the Secret of Porcelain."
>
>I have to say I think this is a wild generalisation Hank. There are other
>factors involved here. IMHO the probable reason the Japanese and Europeans
>stuck with kaolin was purely geological. Hydrothermally altered, low iron
>rhyolites are rare or absent in Europe. As for Japan, I don't know, but
>doubt that the pragmatic Japanese would ignore a plastic petuntse-type rock
>if they had any. And anyway (as I mention above) WE STILL use kaolin base
>clays almost exclusively to make porcelain -and it aint an accident.
>
>Michael Banks,
>Nelson
>NZ
>
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