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Quick Question: Sea Shells - Cone 6 - Which Type?


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#1 Joseph F

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Posted 17 April 2017 - 11:32 AM

As title says what sea shells for cone 6? Does it matter? 



#2 LeeU

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Posted 17 April 2017 - 05:41 PM

 I actually know nothing, truth be told, but  I imagine some nice effects could be gotten from rough, salty shells if perfection is not sought, but the question is how much would the clay pull away and leave cracks or craters, and whether or not that was desired. 

 

Here is a snippet I had read and filed in my "Tips" folder-don't remember the source but do remember reading other comments about the shells holding up when used like wadding, and then turning to powder a few days after firing.

 

Technically, no. You will not be able to use a shell on a pottery vessel and then fire it, with the expectation that the shell will remain in tact and in place, for several reasons (shrinkage rates and the shell will burn out). However....shells are frequently used to prop up pottery vessels during wood firings, this keeps the vessel off the shelf and leaves a gorgeous shell indent in your work. Usually oyster and scallop shells are used for this. A natural glaze forms on the vessel due to the high amounts of ash settling over it, the shells minerals help to add some texture and shape into this glaze forming process."


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#3 Joseph F

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Posted 17 April 2017 - 05:46 PM

Interesting LeeU. I guess I am just going to buy a bunch of random shell types and try them all out. Doesn't seem to be much information on the web about them. Or maybe next time I go to the beach I will try this out and get some free shells. WOoo. Time to schedule a vacation.



#4 alabama

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Posted 17 April 2017 - 09:23 PM

Shells are made from layers with a type of adhesive or bonding agent between the layers. The adhesive burns out above 451 degrees and the layers change to calcium hydroxide over 951 degrees. Calcium hydroxide is a powder that absorbs moisture from humidity, expands, and if there is enough crushed shells in the clay... The vessel will disintegrate with in a year! I know this is true about mussel shell... And assume sea shells are the same/similar!
But then it doesn't hurt to experiment. :)

#5 Joseph F

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Posted 17 April 2017 - 09:24 PM

Thanks for more info. I am just going to test it after I go on vacation this summer. Gonna scoop up a ton of shells with my son then try firing them in bowls and stuff and just see what happens. I was just curious if only certain types worked well, but all the reading I have found seems it doesn't really matter. 

 

So I guess this thread is concluded! 



#6 alabama

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Posted 18 April 2017 - 02:53 AM

The way I use shells the most in the associated with hand built pottery are ribs. If you can find one that is smooth and somewhat oval and the right size, it can be used as a rib. If you flip the same shell over, its a scraper. The shell tool is unlikely to wear out in your lifetime! :). If you find a shell with a wavy edge it can used as a rocker stamp for texture and designs.

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#7 neilestrick

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Posted 18 April 2017 - 09:31 AM

Are you wanting to mix them into your clay or use them to create surface scars like folks do in wood kilns?


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#8 Joseph F

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Posted 18 April 2017 - 09:36 AM

Are you wanting to mix them into your clay or use them to create surface scars like folks do in wood kilns?

 

A little bit of both. Was going to start with the surface scars. Was going to lay pots down on their side, mounted on shells and use glazes that run on the other side so that it wraps around. Then I was also going to mix in shells later on for vase. 

 

I will get to it though. I have so much on my plate right now with my testing. 



#9 alabama

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Posted 18 April 2017 - 07:35 PM

If you didn't know about crushing shells for pottery, you should burn the shells first...then you should be able to crumble them in your hands. As for the percentage, figure 35%-50% or by the look! :). But expect the opportunity to watch it disintegrate after a while.

#10 neilestrick

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Posted 18 April 2017 - 07:54 PM

I would not add them to the clay body. You wouldn't add limestone or plaster chunks to your clay, and this would be about the same. Stick to using them on the surface to produce shell scars in glazes. Any type of shell will work, but the flat scallop shells are the easiest to use, and make for a nice recognizable pattern in the glaze.


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#11 Joseph F

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Posted 18 April 2017 - 09:04 PM

Thanks for info Neil. I will refrain from attempting to mix them into some handbuilt ware.  :ph34r:

 

Found some shells on ebay. Went ahead and ordered them. I will post any good results from my test. Thanks for help everybody.



#12 JBaymore

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Posted 20 April 2017 - 09:26 AM

Being a woodfirer who uses shells a lot as separator wadding (and decoration).....................

 

The impacts of the shells for attractive scarring/marking come from two main factors. 

 

One is that the calcium hydroxide mentioned above turns into calcium oxide at elevated temperatures in the kiln.  Calcium oxide is a powerful flux on silica at high temperatures.  All clay bodies contain silica.  So where the shell material is, it provides a large amount of CaO to react with the SiO2 on the surface of the clay.  This causes some of the silica there to melt.  BUT..... calcium carbonate itself is pretty refractory.  So the vast excess of what is needed to flux the small amount of silica on the surface of the clay acts as a non-melting "separator" wadding.  When stacked on glazed areas, the effect is similar... but the excess of calcium oxide also "matts out" the glaze around the shell where there is "too much" ... and the glaze gets a textural marking that can be nice also.

 

Secondarily, seashells come from........... wait for it.... the SEA.   So when the animals die of natural causes... the shells knock around the ocean for a while before getting picked up on the beach.  The shell surface "deteriorates" a bit since the shell is no longer "living".  The shell get a little more porous... and sea water impregnates the structure a bit.  The sea salt in the shell is another factor in the marking that the shells leave on the clay or glaze.  The sodium compounds in the shell pores volatilize and "flash" around where the shell is... adding coloration to the marks left.  Old beach collected shells are the best for effects.

 

Shells from fisheries don't get the 'knock around the ocean time' after the animal has died.  Seafood is shucked and the shells disposed of.  So they work well... but not as nice as the beach collected shells.

 

Shells from "commercial suppliers" .... as in 'buy them by the pound'....... usually are washed in fresh water during the processing work.  Not as good as fishery shells.  Not as much salt left.  But they work.

 

Typically, the shells are packed with another wadding material inside them.  The shells lose their structure in the firing... so if it is just a shell sitting under something...  the shell will collapse and lose its shape and let the piece over it tip/collapse/fall.  The wadding mix inside the shell is any typical wood firing wadding mix.

 

Now we come to "synthetic shells".  Yes........ a 'make your own' deal.  Some folks make different shaped wadding material that causes effects similar to shells in a wood kiln, but can be different shapes.  The standard mix used is a mixture of 1/2 calcium carbonate and 1/2 plaster of paris.  In the firing in the college's anagama that is cooling right now, one of my students is trying that, but I suggested he also test using salt water for mixing the material up instead of fresh water.   We'll see how that works out next Sunday.

 

To facilitate removing the shell from the fired work. pieces are placed into water and left for a while.  The shells and other wadding material soften and release.  Then some grinding with a Dremel to clean it up and .... done.

 

Note that the dust from the fired shells is not something to get into the air when unloading the kiln.

 

All that being said... I am speaking of firing to anywhere between Orton cone 9 and cone 14.  Have not tried it at cone 6.  Likely "less" impacts.

 

best,

 

......................john


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#13 preeta

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Posted 22 April 2017 - 07:13 PM

for decorative i've used shells as sprigs. used the shells to make a negative and positive imprints. esp since the texture that i like the 'sea creatures' shell thingy is very fragile. 

 

i like doing sprigs because it leaves me the freedom to use as a shell or form other things.

 

i have a couple of giant shells and thought they looked like ribs. never thought about using them as ribs though.


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#14 Joseph F

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Posted 23 April 2017 - 08:55 AM

More good information on shells! I plan on making some small plates and pressing shells into the glaze surface and firing them with the shells on top to see first what happens(purely for testing). Then fire a shell on a plate with a cup on top of it, and just keep going from there. Thanks for the discussions.



#15 Joseph F

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Posted Yesterday, 02:51 PM

So I finally got around to running a test. I just refired a test tile of a glaze combo that I liked with a shell. The results were pretty good to me at least. As promised a picture of the test.

 

This was just a broken shell my son picked up off the beach. The shell was still fully in tact after the firing however it was definitely brittle. This will be perfect for some of the side firings for vases I am wanting to do.  You can see where some of the shell flashed around the topmost shell marking, which is promising.

 

Going to have a blast picking up shells when I go to the beach in July! Wooooo. Gonna take a 5 gal bucket with me. My son will love it for sure.

 

Thanks for all the help everyone.

 

Sea Shell Test


#16 neilestrick

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Posted Yesterday, 03:00 PM

Looks great! Try soaking the piece in water after firing and see if the shell dissolves away. 


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#17 Joseph F

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Posted Yesterday, 03:01 PM

Looks great! Try soaking the piece in water after firing and see if the shell dissolves away. 

 

Doing that now. I am hoping that the brownish part stays, but I have no idea.

 

I will post again in a few days with updates of the water changes.

 

I also forgot to mention the shells I bought didn't do very good. They left marks, but there was no flashing. I am guessing the person who sold them to me had washed them, or as John mentioned they were commercial. It was only like 5 dollars for 100 of them so no loss of value. But just goes to show, nature is really the best maker of things that are beautiful!



#18 neilestrick

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Posted Yesterday, 03:40 PM

Shells that are meant for display are usually boiled and then bleached, otherwise they start stinking pretty quickly. So all the salts will be pretty well gone and limit the flashing.


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#19 JBaymore

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Posted Yesterday, 04:11 PM

Shells that are meant for display are usually boiled and then bleached, otherwise they start stinking pretty quickly. So all the salts will be pretty well gone and limit the flashing.

 

My shell collection 5 gallon buckets when I go to Cape Cod each spring to collect shells smell like a salt flat at low tide.  ;)   Stored outside in the kiln buildings with the lids ON.

 

best,

 

....................john


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Former President and Past President; Potters Council
 

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http://www.nhia.edu/...ty/john-baymore


#20 Joseph F

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Posted Yesterday, 04:13 PM

 

Shells that are meant for display are usually boiled and then bleached, otherwise they start stinking pretty quickly. So all the salts will be pretty well gone and limit the flashing.

 

My shell collection 5 gallon buckets when I go to Cape Cod each spring to collect shells smell like a salt flat at low tide.  ;)   Stored outside in the kiln buildings with the lids ON.

 

best,

 

....................john

 

 

Good Information. I will be sure to take a bucket with a lid and keep it sealed. Woo. Love this place. I don't think I would have ever made it as a potter without these forums. One day I hope when I have decades of experience I can help out the beginners like me.

 

Thanks folks.






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