iandol on sat 2 dec 00
Dear Carol,
Sea Shells are composed of a form of calcium carbonate called aragonite.
Some people use them whole as supports for pots in wood and salt firings =
but I have never heard of them being used in the way you describe. I =
could imagine them being taken from the beach and ground up into a fine =
powder, then weighed out as a substitute for Whiting or Calcite. In some =
parts of the World where there are shallow beaches the sand is often =
powdered sea shell so you may have a source at your toes. During early =
settlement of Australia by Europeans, shell middens left by Aborigines =
were used as a source of lime for mortar when building new settlements. =
Test your beach mud with hydrochloric acid. Take a dried sample, weigh =
it then react with the acid until there is no more bubbling. Filter, dry =
and weight the solid residue. The difference in weights will give you =
the proportion of Calcium carbonate
I pointed out in a letter to CM some time ago that there was potential =
for a hazard in using calcined calcium carbonate as a vehicle to assist =
the distribution of soda in soda glazing in that the dust, if blown into =
a persons eyes, could cause considerable pain and possible corrosive =
damage. So I agree with your assessment.
Best regards,
Ivor
Jim Bozeman on sat 2 dec 00
Carol, I missed your original post but the gist I gather is that you are wondering if one can substitute oyster shells in place of whiting? I've been using oyster shells as part of my glaze ingredients for years. I get them from a local seafood restaurant and let them lie out in the sun for quite a while. The flies and the strong smell warants dumping them aways from your studio. Once they are dried out by the sun I fill a large jar and bisque them to cone 04. Then, after exposed to air for about two weeks or so, they turn to powder. I sieve the powder through 50 mesh and use it in my glaze. In my opinion, it works even better than whiting. I use ten percent. Jim Bozeman
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Christine Caswell on mon 27 sep 04
The discussion about seashells got me thinking...
Has anyone ever tried firing them to say cone 05 electric? I am =
thinking about my middle school students- they would love that. Is cone =
05 hot enough? Or would we end up with a pot with a shell stuck to the =
side of it? Also, does anyone know if they create smoke? I can't even =
put wax resist into the kiln at school for fear of setting off the fire =
alarm!
Thanks in advance for the help!
-Christine Caswell
Maine
Ivor and Olive Lewis on wed 29 sep 04
Dear Christine Caswell,
Sea shells have an organic origin and hence may give of an offensive
odour as residues of ligaments burn away. I say "may" because I have
fired using them only once in a salt kiln and the natural odour of
that kiln would have masked everything else which might "Be on the
nose".
Since sea shells are Calcium Carbonate they will decompose, expelling
Carbon dioxide and leaving a powdery residue of Calcium oxide. Care
has to be taken when removing this because it forms a caustic solution
when it becomes wet.
Once, a very long time ago, I was called upon to spread "Quick Lime"
A change in the wind blew some back into my eyes causing a painful
experience.
This is not a technique I would use in a school situation.
Best regards,
Ivor Lewis.
Redhill,
S. Australia.
----- Original Message -----
From: "Christine Caswell"
To:
Sent: Tuesday, 28 September 2004 8:17
Subject: Seashells
The discussion about seashells got me thinking...
Has anyone ever tried firing them to say cone 05 electric? I am
thinking about my middle school students- they would love that. Is
cone 05 hot enough? Or would we end up with a pot with a shell stuck
to the side of it? Also, does anyone know if they create smoke? I
can't even put wax resist into the kiln at school for fear of setting
off the fire alarm!
Thanks in advance for the help!
-Christine Caswell
Maine
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Louis Katz on wed 29 sep 04
Shells and other calcium compounds can be very dangerous, especially
when nearly pure and when fired above but close to 1500 degrees F.
Calcium Oxide, also know as quick lime reacts violently with water
releasing great amounts of heat. Often it sends framents of the calcium
oxide clumps into the air where if it lands on your eye may do great
damage including what I believe is a likelyhood of blindness.
I do not know whether shells are pure enough to cause this reaction to
proceed quickly enough to cause this to happen, or not. But if I were
firing shells and the kiln failed to get about 2100 degrees I would be
very careful unloading including tight fitting goggles.
Calcium carbonate +heat yeilds Calcium oxide plus carbon dioxide.
Calcium oxide plus water yeilds calcium hydroxide plus heat.
Calcium hydroxide plus carbon dioxide yields calcium carbonate+
water(?) can't check on this at home.
Anyhow be careful with your shells as they come out of lowfire kilns,
and especially be careful if you use whiting wads.
Louis
On Sep 29, 2004, at 6:39 PM, Ama Menec wrote:
> Hi Christine,
>
> At cone 05 they will burn up leaving a white kind of ghost shell
> behind.
> It's basically the ash of the shell and not at all strong. What is
> very odd
> 'tho, if you fire a spiral shell it will come out of the kiln looking
> just
> like a white version of its former self, but after a couple of days
> will
> slowly untwist, and if attached to a pot, may even bring off bits of
> the pot
> as it gently disintegrates. I'm assuming it's moisture doing this but
> I'm
> not certain.
>
> I haven't noticed any smoke when firing shells, but we are in a
> cavernous
> workshop. We'd have noticed if it had been really bad.
>
> Ama, Totnes, Devon, UK.
>
> ----- Original Message -----
> From: "Christine Caswell"
> To:
> Sent: Monday, September 27, 2004 11:47 PM
> Subject: Seashells
>
>
> The discussion about seashells got me thinking...
>
> Has anyone ever tried firing them to say cone 05 electric? I am
> thinking
> about my middle school students- they would love that. Is cone 05 hot
> enough? Or would we end up with a pot with a shell stuck to the side
> of it?
> Also, does anyone know if they create smoke? I can't even put wax
> resist
> into the kiln at school for fear of setting off the fire alarm!
>
> Thanks in advance for the help!
>
> -Christine Caswell
> Maine
>
> _______________________________________________________________________
> _____
> __
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
> _______________________________________________________________________
> _______
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
>
Louis Katz
http://www.tamucc.edu/~lkatz
Ama Menec on thu 30 sep 04
Hi Christine,
At cone 05 they will burn up leaving a white kind of ghost shell behind.
It's basically the ash of the shell and not at all strong. What is very odd
'tho, if you fire a spiral shell it will come out of the kiln looking just
like a white version of its former self, but after a couple of days will
slowly untwist, and if attached to a pot, may even bring off bits of the pot
as it gently disintegrates. I'm assuming it's moisture doing this but I'm
not certain.
I haven't noticed any smoke when firing shells, but we are in a cavernous
workshop. We'd have noticed if it had been really bad.
Ama, Totnes, Devon, UK.
----- Original Message -----
From: "Christine Caswell"
To:
Sent: Monday, September 27, 2004 11:47 PM
Subject: Seashells
The discussion about seashells got me thinking...
Has anyone ever tried firing them to say cone 05 electric? I am thinking
about my middle school students- they would love that. Is cone 05 hot
enough? Or would we end up with a pot with a shell stuck to the side of it?
Also, does anyone know if they create smoke? I can't even put wax resist
into the kiln at school for fear of setting off the fire alarm!
Thanks in advance for the help!
-Christine Caswell
Maine
____________________________________________________________________________
__
Send postings to clayart@lsv.ceramics.org
You may look at the archives for the list or change your subscription
settings from http://www.ceramics.org/clayart/
Moderator of the list is Mel Jacobson who may be reached at
melpots@pclink.com.
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