What the heck is RTV? That's 'room temperature vulcanizing' which in a nutshell is a 2 part silicone mold making compound that cures without any ovens, machines, or other technical stuff. I am in love with this stuff. I first started using it about a year ago to make molds for metal clay. And then a small dim light bulb went off in my head and realized I could use it for molds for ceramic beads.
You can find all sorts of different brands. The one I like is from Cool Tools. It sets up in about 5 minutes and picks up amazing detail. I like that. I like fast. I am impatient. So here's how I use it.
I take my model and anchor it in a slab of plastalina sculpting clay. This model is made of polymer clay but sometimes I use ceramic models that I've bisqued. You can also use found objects like buttons, hardware, etc. But you need to have models with minimal undercuts in the design.
The mold compond comes in two jars and you need to use equal parts of each color. I roll each into a ball adding and subtracting to get roughly the same size. Next the compound gets kneaded together until the colors are blended. It's important not to have streaks in it or the compound will not cure properly. I know this from experience :-(
I then press the mixed compound over the model. I like to start with a rounded surface on the bottom and press from the center out so that no air gets trapped making ugly bubbles. Sorry, no in between photos here. You have to work quite quickly as this brand sets up fast.
Blurry photo of the completed mold.
A little twist of the mold and out pops a naked porcelain star fish.
A couple of tips. If you are using polymer models, buttons, plastic, etc, you don't need to use a mold release. But if you are using a bisque or otherwise porous model you may need to use a mold release. I use a Cool Slip from Cool Tools, used with metal clay. That's what I have on hand so it's easy.
Dust your mold with corn starch to keep the clay from sticking and making a horrible mess of your work.
This type of mold isn't going to work well for flat things that have a tendency to warp. That's because you do end up twisting the clay a bit as it comes out of the mold. But it's great for beads.