Firing seashells in clay

[MarkS]

My wife has made a plate/plaque with seashells embedded around the rim.

I'm sure how yo fire it or if there are any precautions to be taken.

I normally fire bisque to ^04 and glaze at ^6.

Thanks in advance!

[icyone]

make a small tiny test with a shell imbedded and test that first maybe

[JLowes]

Uh oh! I think you may have a problem there. In wood and gas firing, folks sometimes use seashells, filled with wadding to sit the pots on so the glaze can run onto and over the shells and not stick to them, as a decorative efffect, or to just keep the pot from sticking to the shelf. This works because the calcium in the seashell makes then refractory, and at high temperatures the calcium in the seashells changes chemically such that after the firing it is a powder that can be easily removed. I expect that even at Cone 04 this may occur, but certainly Cone 6 would make the transformation.

 

I am assuming that the idea is to have the seashells intact after the firing. I am afraid they will break down in the firing. Maybe one of our more experienced members will know if this is the case at Cone 04.

 

A picture of such pots is shown here:

 

http://www.dicklehma...?pottery_id=908

 

http://www.dicklehma...?pottery_id=907

 

John

[Marcia Selsor]

I have a low fire plate from Portugal

with shells on it. I would say it is about ^04 or ^06.

The shells should be ok. I have noticed that shells along the Baltic sea were paper thin 20 years ago. Shells along the Gulf of mexico near where I live are

a lot thicker. So choose your shells well.

Marcia

 

 

 

[Guest alabamapotter]

Hey,

You have 2 choices. 1. take the shells off and add them after you fire the plaque and 2. Fire the entire plaque below 951 degrees F.

 

Over firing will cause the shell to turn from shell to calcium hydroxide which will absorb moisture from the humidity over the next 6 months and

turn to dust. So the choice is yours. Your best bet is to add them later, since even if you, say, fire the plates below 951, you'll still

burn out the adhesive/glue (for lack of a better word) that hold the sheets of calcium together.

 

Shell has been added as a temper for several centuries in the USA. The pre-historic Mississppian culture and the historic Iroquois, Chickasaws, Choctaws, Cherokee,

and Upper-Creeks plus others, added crushed shell to their pottery but knew how to control the temperatures for the most part.

 

Hope this helps.

Alabama Potter

[MarkS]

Well, I certainly got some food for thought.

I may try a low firing and see what happens. Nothing lost at this point.

I was more worried if it would explode.