How to fire large sculptures (newbie)

[OlgaBiff]

Hello.

I just made a large sculpture and plan to make more in the future. I need some advice on how to place it in the kiln. I have made some holes underneath so the steam can exit the piece... This may be a very naive question, but I do I place it inside the kiln? Should it lay on one side? What's the best way to fire it so the steam escape properly and the piece don't explode?

Thanks so much for your help. Hope this topic may be helpful to others too.

 

[JohnnyK]

Hi Olga...That is a beautiful and intriguing sculpture! As for firing it, it should be absolutely, positively bone dry before you even think of putting it in the kiln because if you're worried about the steam escaping properly you'll be looking at an explosion. What are the dimensions of the piece and, except for the holes in the bottom, is it solid? If so, it will take a long time to get to the bone dry state.

[Chilly]

2 hours ago, OlgaBiff said:

What's the best way to fire it so the steam escape properly and the piece don't explode?

As Johnny says, make sure it is absolutely, completely, totally dry.

One problem with drying thick pieces:   as the outer surface dries, it shrinks and makes a crust. The inner moisture now has more and more difficulty evaporating to the outside.

 

Fire it very, very slowly so the moisture can escape slowly.

Depending on the clay body, you can probably fire it anyway up that fits in the kiln.  So long as it is dry.

[Min]

@OlgaBiff, how thick are the walls on your piece? What's the thickest part? I would make a perforated slab for it to fire on made from the same claybody as your sculpture with holes made in the slab. Have a look at Beth Cavener's firing schedule. She single fires to cone 2 with an extremely long 16 step firing schedule. She loads the kiln while the pots are still leatherhard then dries them in the kiln for up to a week before firing with multiple long holds. Reason for loading while the pieces are still leatherhard is it isn't as fragile as moving a bone dry piece. If your piece is at all tippy I would make a perforated cradle for it to fire in as Cavener does.

 

[OlgaBiff]

Thank you all!

It is bone dry and it is hollow inside. I build it using coils and the walls are not particularly thick. I am only used to fire vases for now. Since the holes for the steam to escape are at the bottom in this case should it lay on one side?  Or perhaps making holes at the bottom is not even necessary...?  

46 minutes ago, Min said:

I would make a perforated slab for it to fire on made from the same claybody as your sculpture with holes made in the slab

 

[Min]

Steam will escape from the walls regardless of whether there are holes in the base or not. What the holes would probably do though is help the piece while drying out. Re firing on it's side or not, is there a concern about slumping? Is this a lowfire clay?

[OlgaBiff]

 

4 minutes ago, Min said:

Steam will escape from the walls regardless of whether there are holes in the base or not

Thank you! That is what I wanted to ask but perhaps difficult to express in a foreign language.

It's white stoneware with 40% of grog. It is pretty stable I think, I have no concerns for it to slump/fall. Only to crack or explode for the steam trapped inside. But for what I understand if your firing schedule is slow enough you could fire a closed sphere?  

1 hour ago, Min said:

I would make a perforated slab for it to fire on made from the same claybody as your sculpture with holes made in the slab.

Maybe this kind of support could be helpful too?

 

[Min]

I don't think you need the stilt if the piece isn't glazed on the bottom. Reason the slab made from the same clay works is that it shrinks at the same rate as the clay during the firing.

"But for what I understand if your firing schedule is slow enough you could fire a closed sphere?" Yes, although a hole will help it dry out faster.