Can I modify ceramic once it's out of the mold ?

[Dalva88]

Hello,

I would like to make a plaster mold for a big (34cm) 3D printed grenade. The problem is that the shape is so complicated that making a two, or three parts plaster mold wouldn't work.

So I was wondering is I could "fill in" the complicated parts with play-doh or something (the part of the grenade with all the squares, to make it simply round and smooth and easy to cast) to then, later on, cut those squares and sculpt them out of the dry clay. 

 

Or would it be to late ? (is there some stage when I take out the clay out of the mold when it's solid, but still not complitely dry and can be worked on ?)

 

Thanks so much for your help, I've been struggling with this, trying to find a way.

[Rebekah Krieger]

What kind of mold are you using? Casting liquid slip or a press mold?

if using a press mold I recommend using something slippery on the inside (dawn dish soap works) to keep it from sticking to they play doh. 

 

If using slip cast, I think timing is critical. You don’t want your piece to get too dry to alter but yet it needs to be dry enough to release from the mold. 

[JohnnyK]

How many grenades do you plan on making? If you look to slip cast and carve, you will probably have a problem with the wall thickness not being thick enough to carve. You might be better off hand building and sculpting the grenades, or throwing and carving the bodies and adding the other pieces...

[Dalva88]

I'm using liquid plaster. 

Yes exactly, i don't want it too dry, but still dry enough to be solid.

Thanks for your reply. I just wanted to know if such a thing was possible, if it is I can go through some trial and error to make it work

[Dalva88]

2 minutes ago, JohnnyK said:

How many grenades do you plan on making? If you look to slip cast and carve, you will probably have a problem with the wall thickness not being thick enough to carve. You might be better off hand building and sculpting the grenades, or throwing and carving the bodies and adding the other pieces...

 

I'm doing it by hand also, but ideally I would like a mold to make as much as I want. 

I would also like it to be geometrically perfect all round, and doing this by hand is almost impossible (or I don't have the skill) 

[Min]

I would use paperclay for the additions after the piece is removed from the mold. If you use the same clay to make the paperclay as your slip is made from (without the deflocculants) there won't be an issue with glaze fit etc. 

[Dalva88]

I don't know if making additions is the way to go, I'm afraid it would come appart....

About the wall thickness, to avoid it being not thick enough to carve, would it be possible to just not empty the excess liquid porcelain (like when you make a vase, to hollow it out) but just carve out the inside once I take out the cast ? (so it's just a LITTLE hollow and doesn't break when fired)

[Rae Reich]

Try one!