chris clarke on tue 13 nov 01
Hey guys,
I've been pouring over my books and organizing my thoughts on carbon =
trapping in shinos. I'd read somewhere a potter referring to the glazes =
getting 'sticky' early in the firing and catching carbon. I'm not sure =
if sticky is a chemistry term, so in the interest of me getting better =
results I've began a quest.=20
I noticed a coincidence that seems to mean something but I'm not sure. =
In both Mel's and Tony's articles they both stated that early reduction =
for carbon trapping should begin around ^011 or ^010. The coincides =
with the final decomposition of all remaining non-oxides which is around =
900 C or 1652 F. I think that nothing is 'sticky' without chemical =
something or other, after all everything is chemistry ain't it.
Is there some kind of swap out during this time? Has anyone actually =
looked at what this carbon trapping looks like under analysis?? =
Chemistry was never my subject but I have a basic knowledge so I know =
something has to cause carbon to be trapped. Anyone got a more solid =
answer then magic?
chris
temecula, california
chris@ccpots.com
www.ccpots.com
John Baymore on wed 14 nov 01
Chemistry was never my subject but I have a basic knowledge so I know =
something has to cause carbon to be trapped. Anyone got a more solid =
answer then magic?
chris,
Voodoo .
Seriously, there is a copy of an old article I published in a print venue=
up on my website in the "Of Interest to Potters" section that you might
find has some relevence to this subject. It is titled something like "So=
me
other considerations in ......." or something like that . It explains=
one of the ways that a glaze like a shino gets "sticky".....has a very lo=
w
temperature melting surface that can effectively "trap" carbon within the=
more refractory and "open" layers just below the surface.
Might be of use to you.
Best,
..............................john
John Baymore
River Bend Pottery
22 Riverbend Way
Wilton, NH 03086 USA
603-654-2752 (s)
800-900-1110 (s)
JohnBaymore.com
JBaymore@compuserve.com
John.Baymore@GSD-CO.com
"Earth, Water, and Fire Noborigama Woodfiring Workshop 2002 Dates TBA"
Dave Finkelnburg on wed 14 nov 01
Chris,
When a hydrocarbon fuel-fired kiln is sufficiently starved for oxygen,
some of the carbon compounds are reduced to pure carbon inside the kiln.
That carbon then condenses onto items in the kiln which are cooler than the
kiln gases--namely the ware. IF the kiln is held in reduction from this
point until the glazes melt, the carbon is "trapped" under the glaze, where
it stays, even if the kiln is then thrown into full oxidation.
So carbon trapping is simply a matter of forming pure carbon in the kiln
with heavy reduction, and then maintaining a reducing atmosphere until a
liquid glaze seals in the carbon and keeps any oxygen from burning the
carbon away.
Regards,
Dave Finkelnburg
From: chris clarke
I've been pouring over my books and organizing my thoughts on carbon
trapping in shinos. I'd read somewhere a potter referring to the glazes
getting 'sticky' early in the firing and catching carbon. I'm not sure if
sticky is a chemistry term, so in the interest of me getting better results
I've began a quest.
I noticed a coincidence that seems to mean something but I'm not sure. In
both Mel's and Tony's articles they both stated that early reduction for
carbon trapping should begin around ^011 or ^010. The coincides with the
final decomposition of all remaining non-oxides which is around 900 C or
1652 F. I think that nothing is 'sticky' without chemical something or
other, after all everything is chemistry ain't it.
Is there some kind of swap out during this time? Has anyone actually looked
at what this carbon trapping looks like under analysis?? Chemistry was
never my subject but I have a basic knowledge so I know something has to
cause carbon to be trapped. Anyone got a more solid answer then magic?
chris
Hank Murrow on thu 15 nov 01
John Baymore wrote about shino 'stickiness';
>Seriously, there is a copy of an old article I published in a print venue
>up on my website in the "Of Interest to Potters" section that you might
>find has some relevence to this subject. It is titled something like "Some
>other considerations in ......." or something like that . It explains
>one of the ways that a glaze like a shino gets "sticky".....has a very low
>temperature melting surface that can effectively "trap" carbon within the
>more refractory and "open" layers just below the surface.
And Hank suggests;
That the soluble fluxes like soda ash, which are deposited on the
surface of the glaze as it dries may be the source of the 'stickiness'. I
don't see this carbon trapping happening in glazes which contain no soluble
material.
Kenneth J. Nowicki on fri 16 nov 01
Thank you Dave for an easy to understand explanation of this whole carbon
trap effect with Shino glazes. I am just beginning to learn about Shinos and
this helps a great deal.
God I love this list! :-)
Ken
in Encino, CA (soon to be Port Washington, NY)
..............................................................................
..............................
> When a hydrocarbon fuel-fired kiln is sufficiently starved for oxygen,
> some of the carbon compounds are reduced to pure carbon inside the kiln.
> That carbon then condenses onto items in the kiln which are cooler than the
> kiln gases--namely the ware. IF the kiln is held in reduction from this
> point until the glazes melt, the carbon is "trapped" under the glaze, where
> it stays, even if the kiln is then thrown into full oxidation.
> So carbon trapping is simply a matter of forming pure carbon in the
kiln
> with heavy reduction, and then maintaining a reducing atmosphere until a
> liquid glaze seals in the carbon and keeps any oxygen from burning the
> carbon away.
> Regards,
> Dave Finkelnburg
chris clarke on fri 16 nov 01
Thanks guys, this being my second shino question, first one never answered,
I started to think I wasn't being allowed in the club, but that's never
stopped me before.
I'm starting a series of tests soon, just got the twenty or so jars done to
be put in several firings with five shinos that have worked in the past. I
found that not only soda ash but wood ash also works for carbon trapping. I
assume it's the 'black water' that develops on the top of it so I'll be
checking that out. Pretty sure it's some kind of soluble material since I
don't wash it.
After those I'll be adding humidity to the kiln. Haven't decided whether to
fire all twenty in one firing so I know they've all gotten the same workout
or fire them separately with a set schedule. Don't think I will load them
all in for fear I screw the pooch on that day and have to start over but it
is a thought.
Thanks again for everyone who answered me,
chris
temecula, california
chris@ccpots.com
www.ccpots.com
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