Air in Pieces

[DaniBanani]

Hello! I am learning and exploring more with Hand building however I have a doubt that I’m not sure if is a bit silly.

I’m interested in making something that has a thick base but i have hollowed it out since I know elements that are too thick will not do well, The bottom of the base is closed off but on top of the hollowed out top i want to attach a bowl. By attaching the bowl, am i creating a giant pocket of air that will cause this to explode? Or since they are separate pieces being attached should it fire well?

[DaniBanani]

thanks in advance

[Kelly in AK]

In a situation like this most people put a pinhole through the closed off part. That’s all you need, just a pinhole. Put it in a place that won’t be glazed. You can count on it cracking if you leave it sealed off. 

[Babs]

Holes in the base will aid drying for sure. It is moisture not trapped air whih will nlow a piece apart. So is base is thick , pierce it to allow i todry out.

[Bill Kielb]

7 hours ago, DaniBanani said:

The bottom of the base is closed off but on top of the hollowed out top i want to attach a bow

As Kelly mentioned if this is completely closed and sealed definitely include a pinhole. I assume that means clay will run continuously under the bottom of this so it can also drag on the shelf with lots of friction when fired. You may want to add grog or a bit of alumina under it when firing to lessen the drag or friction on the shelf so it can shrink freely and evenly as it fires to prevent it from cracking as it shrinks. A salt shaker or even sprinkling type spreading is usually just fine.

[DaniBanani]

Thank you for your help! i did include a pinhole but i wasn’t sure if it was enough

[oldlady]

if the base is that thick, an opening of at least a quarter of an inch that will not be glazed will help the item dry.   drying completely will take a long time so putting the base onto something absorbent, like drywall, will help it dry evenly.  if, after a while, the drywall looks dark, move the piece to a dry section of drywall.  you do not want to blow this up in your kiln so be sure it is absolutely dry before firing.

[DaniBanani]

thank you all! i appreciate the advice 

[neilestrick]

Air pockets of any size will not cause explosions. Air doesn't increase in volume enough to blow apart clay. However with a closed piece, whether completely closed or with a pin hole, it can take a really long time for it to dry completely because there's little to no air flow on the inside. It can be bone dry on the outside and still leather hard on the interior. So you need to dry it for a long time and do a good long preheat in the kiln to make sure it's totally dry before taking the temp up. Otherwise you risk steam explosions. This is why people think you can't fire a closed form. They think it's dry (but it's not), it blows up, must be because it was closed! Nope. You can fire a totally closed hollow piece just fine, it just takes forever to dry out. The pin hole will relieve air pressure building up in the piece as it shrinks during drying and firing, which can cause distortion in clay bodies like porcelain, which soften up during glaze firing. I've seen porcelain pots inflate slightly during glaze firing due to the air pressure.

[Pres]

I agree with all of the above, but after working with student pots for years, I noticed that poorly created joins have a tendency to separate where there is trapped air. Often these joins would not have separated if not having trapped air.

 

best,

Pres

[Babs]

If the design of  pot doesn't need the extra weight of a closed base, after joining,  the base could be carved away, or the "base" could be thrown without a base , as it were.