My wife confessed to me today that she really missed her bump and though we plan on having more children, that is still several years away. It got me thinking though. We did a plaster belly cast at around 37 weeks and I was thinking I could use it to make a silicon belly for her. She seemed thrilled with the idea (lucky me!), but now comes the task of making it. 

I'm not sure the best way to use the plaster mold without ruining it or how to really go about it in general. If anyone has any experience or advice I'd be happy to take it.

I'm in a similar situation where I've been wanting to commission a pregnant model to make a cast if only so we could use it as a mold for when she isn't pregnant.

I've found that the first thing you do after picking a material to make a mold positive from the cast being used as a negative is to use some sort of release agent so that the rubber or other casting material does not stick to the mold to the point of damaging either it or the casting.

With that said, liquefied gelatin makes a decent mold, so that you could potentially use it instead of your actual belly cast. For a vegan alternative, as gelatin is made from hooves, I hear there's stuff called Agar Agar, that is made from seaweed collagen.

Here is a tutorial showing how gelatin can be used for a negative mold.

hxxps://www.youtube.com/watch?v=MIj_I6mW5QQ (Part 1)

hxxps://www.youtube.com/watch?v=wyxpYWvGU2Q (Part 2)

This is the cheapest mold making material, and can be remelted and reused. It tends to stink though so it is advised to use some essential oils to make it smell better should you also want to try to use it as a prosthetic. It melts when it gets warm so it is advised to use a glue substance called pros-aid to lengthen the life of any prosthetic/mold made of gelatin.

You might also get some use from polyurethane foam to make a belly positive cast using your plaster mold. To support the plaster mold you have, you can use sand set in a sand box like configuration, maybe placing plastic bags as a barrier to make sure the sand does not abrade the cast.

As for the polyurethane, here is a demonstration using fence post mix.

hxxps://www.youtube.com/watch?v=7JJYFSCpj9s

I figure with your belly cast properly supported and coated with release agent (cooking spray, or Vaseline), a polyurethane pour would be the way to make a mold positive out of your plaster cast's negative.

And then perhaps use a "paint on" molding method to cast a new negative from the polyurethane positive, so that you might no longer need to use your plaster belly cast, though that probably has the very best detail.

Then you pretty much have a two piece mold and then just have to sit one inside the other and find a way to make a few centimeters gap between them in to which to pour your silicone.

Something like small pegs placed at the bottom and sides to make a gap. This will cause a couple holes in your final product but from what I've heard those can be filled in/covered up with more silicone.

That's what I'd like to try with all these mold making tutorials on youtube.
hxxps://www.youtube.com/watch?v=pY-6vlJvnZg
There's also slip casting using latex.



Not sure how well latex itself could be used for a mold for silicone, but there's always the prospect of pouring heated gelatin over that , provided you cover the latex in a protective coating so the hot gelatin doesn't wreck it.

hxxps://www.youtube.com/watch?v=_D2Kv7DXXDo&t=140s

hxxps://www.youtube.com/watch?v=kLqQ--tDlYY

(July 6, 2023, 12:07 pm)pregwyrm I'm in a similar situation where I've been wanting to commission a pregnant model to make a cast if only so we could use it as a mold for when she isn't pregnant.

I've found that the first thing you do after picking a material to make a mold positive from the cast being used as a negative is to use some sort of release agent so that the rubber or other casting material does not stick to the mold to the point of damaging either it or the casting.

With that said, liquefied gelatin makes a decent mold, so that you could potentially use it instead of your actual belly cast. For a vegan alternative, as gelatin is made from hooves, I hear there's stuff called Agar Agar, that is made from seaweed collagen.

Here is a tutorial showing how gelatin can be used for a negative mold.

hxxps://www.youtube.com/watch?v=MIj_I6mW5QQ    (Part 1)

hxxps://www.youtube.com/watch?v=wyxpYWvGU2Q  (Part 2)

This is the cheapest mold making material, and can be remelted and reused. It tends to stink though so it is advised to use some essential oils to make it smell better should you also want to try to use it as a prosthetic. It melts when it gets warm so it is advised to use a glue substance called pros-aid to lengthen the life of any prosthetic/mold  made of gelatin.

You might also get some use from polyurethane foam to make a belly positive cast using your plaster mold. To support the plaster mold you have, you can use sand set in a sand box like configuration, maybe placing plastic bags as a barrier to make sure the sand does not abrade the cast.

As for the polyurethane, here is a demonstration using fence post mix.

hxxps://www.youtube.com/watch?v=7JJYFSCpj9s

I figure with your belly cast properly supported and coated with release agent (cooking spray, or Vaseline), a polyurethane pour would be the way to make a mold positive out of your plaster cast's negative.

And then perhaps use a "paint on" molding method to cast a new negative from the polyurethane positive, so that you might no longer need to use your plaster belly cast, though that probably has the very best detail.

Then you pretty much have a two piece mold and then just have to sit one inside the other and find a way to make a few centimeters gap between them in to which to pour your silicone.

Something like small pegs placed at the bottom and sides to make a gap. This will cause a couple holes in your final product but from what I've heard those can be filled in/covered up with more silicone.

That's what I'd like to try with all these mold making tutorials on youtube.
hxxps://www.youtube.com/watch?v=pY-6vlJvnZg
There's also slip casting using latex.



Not sure how well latex itself could be used for a mold for silicone, but there's always the prospect of pouring heated gelatin over that , provided you cover the latex in a protective coating so the hot gelatin doesn't wreck it. 

hxxps://www.youtube.com/watch?v=_D2Kv7DXXDo&t=140s

hxxps://www.youtube.com/watch?v=kLqQ--tDlYY

Wow, thanks for such a detailed response! I'll definitely check those videos out and let you know how it goes.