[Clayart] Firing deep bowl-like sculpture

[vpitelka at dtccom.net]

Hi Kathy - 
At the Appalachian Center for Craft we stopped using sand or grog under flat-bottom items during firing, because we saw so many of them crack or pop.  The sand insulates the underside from temperature changes, and that can be problematic during heating and cooling.  In contrast, wadding allows heat and atmosphere to pass beneath the piece. 

So much depends on the claybody and the size and shape of the piece.  Why are you assuming that this piece needs special support?  I am assuming you are talking about the final firing, and I am assuming the underside is unglazed.  If you are sure it needs special support, I would just use a network of wadding.  

For any firing that is not salt or soda, you can make wadding out of 50-50 china clay and flint, and those are inexpensive materials.  Place the wadding right on the kiln shelf where the surfaces of the piece are close to the kiln shelf, and place the wadding on kiln posts elsewhere.  I guess you can't overdo that.  Use as much support as you think it needs.  If kiln posts seem too precarious, use quarter bricks or half bricks, whatever combination gives you the height you need while providing greater stability.  
- Vince

Vince Pitelka
Professor Emeritus of Art/Ceramics
Appalachian Center for Craft
School of Art, Craft & Design
Tennessee Tech University
Now Residing Chapel Hill, NC
vpitelka at dtccom.net
www.vincepitelka.com 

-----Original Message-----
From: Clayart <clayart-bounces at lists.clayartworld.com> On Behalf Of Kathy Forer
Sent: Monday, February 17, 2020 5:24 PM
To: clayart at lists.clayartworld.com
Subject: [Clayart] Firing deep bowl-like sculpture

I’m firing a large bowl-like structure that has walls and planes inside and some perforations to the bottom outside. The overall shape is  is an 18” shallow bowl. 

I will put sand underneath, thanks Snail, (regular sand, special fine silica sand?) and was considering a collar of a few supports, lumps of clay or kiln furniture, 1/3 of the way in from the rim. it pretty much can sit on its bottom. 

Is that all I need to do? Thanks!

Kathy


Kathy Forer
Kathyforer.com

Sent from my iPhone