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sea shells and sagger fire

updated wed 30 apr 97

 

PurpleLama@aol.com on sat 29 mar 97

I just returned from my first trip to LA and San Diego. I had a great time
and spent hours on the beaches walking and collecting shells. I found some
shells and pieces of shells that I would like to integrate into some of my
clay projects. specifically, I'm in a sagger fire workshop at the Baltimore
Clay Works over the next few weeks and was thinking I would include the shell
pieces some of my sagger fired pieces. However, I have several questions:
- Has anyone included shells in pieces that they have sagger fired? What
were your results?
- Do the shells disintegrate? If so, are that different colors? If not, what
is left?
- Have you had experience with firing shell pieces at different
temperatures? We will fire one load to cone 010 or lower and another cone 06
or higher. Will the results from the two fires vis a vis the shells be
similar?
- Should the shells go through the bisque firing or be added for the final
firing only?
- Any other advise or speculation?

Thanks for your help.

Shula in Baltimore, Maryland
wishing she was back on the beach in southern California!

Marcia Selsor on sun 30 mar 97

I think you'll find shells will become calcium carbonate AKA whiting.
Marcia Selsor


PurpleLama@aol.com wrote:
>

> - Has anyone included shells in pieces that they have sagger fired? What
> were your results?
> - Do the shells disintegrate? If so, are that different colors? If not, what
> is left?

> - Any other advise or speculation?
>
>
>
>
--
Marcia Selsor
http://www.imt.net/~mjbmls/
mjbmls@imt.net

Jon Lovejoy on sun 30 mar 97

I found some shells and pieces of shells that I would like to integrate into
some of my clay projects.
- Has anyone included shells in pieces that they have sagger fired? What
were your results?
- We will fire one load to cone 010 or lower and another cone 06 or higher.
Will the results from the two fires vis a vis the shells be similar?
- Should the shells go through the bisque firing or be added for the final
firing only?

PurpleLama - (purple llama?)

I have taken impressions from rocks along the Southern California coast and
often pick up bits of shell in the clay. The shells do last through the
bisque and the raku firings, but some shells lose some of their
color/iridescence. When the clay is wet, I have embedded small pieces of
shell (small so the shrinkage won't crack the piece) and had great success.
Have fun!

Jon in CA

Richard Selfridge on sun 30 mar 97

Shula, I may not be of much help about the low or sagger firing of the
shells, but we have used them extensively in hi fire wood (cone 11-12). The
material you have in the shells is almost pure calcium carbonate, that is
except for the residual salt from the sea water. When you calcine the
shells, that is at a low bisque temp. they will become friable, that is soft
and powdery and lose their shape integrety. We use them at high temp. to
seperate stacked ware in the wood kiln.
They leave delightful scars on the ware from the fluxing of the
residual salt which makes a glaze where the shell meets the plate. We put
refractory wads inside the half shells to maintain the distance between the
pieces because the shells by themselves will become a flat dusty powder and
the wadded foot would stick to the plate below. Calcium carbonate is fairly
refractory in its pure state so they do a good job of seperating the pieces.
Visually, we like the way these scars prepare a clay blank for the
kind of drawing we wish to put on them, much like a piece of hand made
paper. If you want to see some examples of this look on our Web site at
http://www.compusmart.ab.ca/selfridg I don't think I would introduce the
shells into the clay body itself because the effect would be like a lime pop
which shows up when the atmospheric water,(humidity) is reabsorbed, swells
and pops out. "Who is the patriarch of the potters? Plaster Pops of course"
Hope this helps.
Richard and Carol Selfridge
http://www.compusmart.ab.ca/selfridg
selfridg@compusmart.ab.ca

JanetH13@aol.com on sun 30 mar 97

I've only tried sagger firing once in a workshop, but the teacher suggested
shells among other organic materials as things to include in the sagger. I
was very happy with the results. My best piece was a mask. One area where I
set the shell has a blackened shape which corresponds to the shell. I had
used a copper stain (I think it was water with copper carbonate added) on the
piece, and where the shell covered it, I got a reddish mauve
color--apparently the shell created a tiny area of reduced atmosphere. Other
parts of the mask with the copper stain were greenish, as if oxidized.

We didn't use shells in the bisque, only in the final fire. I don't remember
if the shells disintegrated, but I don't think they did.

I suggest you experiment with shells in your sagger firing. I think you'll
be happy with the results.

Janet

Fay & Ralph Loewenthal on sun 30 mar 97

Shula, I live in a coastal city so have lots of opportunity
to pick up shells and have done. I have never fired them
in a piece, but have noticed that they seem to be mostly
calcium. They disentegrate and together with seaweed I
made a terrific ash glaze (I just have to repeat it?).
Maybe if covered with glaze and only put them onto the
piece in the glaze firing they would remain whole?
Good luck and enjoy the workshop Ralph in PE SA

Fred Paget on tue 1 apr 97

PurpleLama@aol.com wrote:
>Has anyone included shells in pieces that they have sagger fired? What
> were your results?
A few years ago I needed some lime for Mexican cooking (Making hominy from
corn for postole) and lacking any other source of calcium carbonate I fired
a large conch shell to cone 05. The result was beautiful white quicklime
(Calcium oxide). Adding a little of this to water made some nice pure lime.
Quick lime reacts with water to form a good deal of heat and results in
slaked lime - Calcium hydroxide. If you leave it out in the air it will
slake from the water vapor it picks up from the ambient air.
If you imbed a whole shell in your work it will make a mess.


Fred Paget---Mill Valley,CA,USA

Evan Dresel on wed 2 apr 97

At 06:58 AM 4-1-97 EST, you wrote:
>----------------------------Original message----------------------------

>A few years ago I needed some lime for Mexican cooking (Making hominy from
>corn for postole) and lacking any other source of calcium carbonate I fired
>a large conch shell to cone 05. The result was beautiful white quicklime
>(Calcium oxide). Adding a little of this to water made some nice pure lime.
>Quick lime reacts with water to form a good deal of heat and results in
>slaked lime - Calcium hydroxide. If you leave it out in the air it will
>slake from the water vapor it picks up from the ambient air.
>If you imbed a whole shell in your work it will make a mess.
>
>
>Fred Paget---Mill Valley,CA,USA

That's great! Personally, I would have just gone to the grocery.

If you decide to make a habit of this, you might consider that many shells
have reasonable amounts of strontium in them. Enough that I might worry
even though we generally consider strontium to be much less toxic than
barium. Interesting geochemistry actually -- the crystal structure of the
aragonite form of CaCO3 is more "open" than calcite so more strontium can
squeeze in. Many shells contain aragonite as well as calcite. As sediments
are compressed into limestone the aragonite present in shells turns to
calcite and the strontium is booted out.

-- evan who is just trying to keep the traffic up while all those folks are
having fun in Las Vegas.

pedresel@revolution.3-cities.com