[Clayart] Sea shells in the kiln?

Vince Pitelka vpitelka at dtccom.net
Tue Jan 3 08:11:57 EST 2017


Hi Fred - 
Maybe there was a bit of a misunderstanding.  You are apparently using shells under unglazed porcelain, perhaps because of porcelain's tendency to "pluck."  I am not aware of anyone else using shells on unglazed surfaces except in salt, soda, and wood-firing.  Most people use shells on glazed surfaces, and I am quite sure that is what Ken was referring to.  In that case, the shell impressions will leave a sharp edge around the impression that would need to be ground and would certainly be seen as a defect in electric-fired work if the ground surface was not polished.

In all the time I have seen shells used to support pots, I have never been aware of anyone using anything other than the small half-round shells with the classic seashell fluting or grooves that leave the desirable impression in the glaze surface, and those ones must be packed with wadding or they will collapse in the firing.  I like your suggestions of other shapes to use in place of wadding or stilts, but I have not personally seen that done.  Your suggestion of marble or limestone tile cut with tile nippers is very clever, and I will remember that.  

Your property in Mill Valley sounds amazing.  
Thanks - 
- Vince

Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka at dtccom.net  
https://sites.tntech.edu/wpitelka/
 


-----Original Message-----
From: Clayart [mailto:clayart-bounces at lists.clayartworld.com] On Behalf Of Fredrick Paget
Sent: Sunday, January 1, 2017 12:26 PM
To: Clayart international pottery discussion forum <clayart at lists.clayartworld.com>
Subject: Re: [Clayart] Sea shells in the kiln?

Hi Vince,
  The need for wadding depends on the type of shell.  A small cone shell does not need ii as the inner shape is a spiral and waddding would not go up in it very far any way. Small cone shells from the shell shops in Florida used to be cheap, but I have not checked lately. They are endangered in California and collection is prohibited. When I was young and a skin diver there were plenty of them and I still have a small bag of them collected in the  1950’s . 
  I only use them in cone 10 firing of pots that are not glazed on the bottom. Stilts used in low fire are not suitable for cone 10 but the Calcium oxide  (quick  lime) is not melted at all in normal hi fire, The melting point is over 4000 deg F.

  As I posted a few months ago you can make cone ten stilts out of marble of limestone tiles with a pair of tile nippers. I frequently use shel or limestone stilts in cone 10 porcelain firing in my electric kilns.  I am not using my gas kiln and have not used it in 16 years since my accident .Anybody want to buy. it?  Cheap? There is a picture of it in Mel's kiln book.

 Since on my death this property will probably be sold and bulldozed to get rid of my studio, kilns, greenhouses and storage buildings,  some 50 small fruit trees and a Mill Valley Mansion of 2 0r 3 stories height erected as has been done on about half of the lots on my sub divsion already. We are just over the bridge from San Francisco an prime real estate on the sunny side slope of the ridge,40 feet above sea level. There are investors who do that and sell it. We call it  “flipping the property"

The marking on an unglazed bottom is easy to grind off and is not a defect in my opinion.

Fred.

On Jan 1, 2017, at 5:18 AM, Vince Pitelka <vpitelka at dtccom.net> wrote:


Hi Ken -
All the answers about shells are accurate, except that no one mentioned that you cannot support pots just on shells, because the shells will lose their structural integrity and collapse.  They must be filled with wadding.  For an electric firing, the wadding can just be a 50-50 mix of flint and china clay.  For salt, soda, or wood, we generally use a mix of 50 alumina, 40 china clay, and 10 ball clay.  Just pack the open side of the shell with wadding .  

Keep in mind that the only reason to do this in an electric firing would be if you specifically wanted the impression of the shell in the surface of your glaze.  The glaze conforms to the surface of the shell, and as others have mentioned, when soaked in water, the calcined shell washes away.  Around the edges of the contact surface you usually end up with sharp edges that are ground or sanded a bit to take off the sharpness.  On a wood-fired pot, those ground areas are generally not seen as a defect, but on an electric-fired pot they likely would be, and you'd have to go to considerable trouble to polish those ground area with a buffing wheel and polishing compound.  That would be a lot of work and I cannot see any advantage.  I have never heard of anyone using shells in an electric kiln, but you might come up with a situation where it is worthwhile and effective.
- Vince

Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka at dtccom.net
https://sites.tntech.edu/wpitelka/




-----Original Message-----
From: Clayart [mailto:clayart-bounces at lists.clayartworld.com] On Behalf Of Ken Chase
Sent: Saturday, December 31, 2016 5:01 PM
To: clayart at lists.clayartworld.com
Subject: [Clayart] Sea shells in the kiln?

Saw an exhibit of pottery where some of the Wares were set upon their sides on sea shells Which left an imprint. I'm a novice but I'm sure It was a wood firing or salt. Can sea shells be used in a similar fashion in an electric kiln?
And how much heat can sea shells take?
Thanks.
Ken

Sent from my iPad
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