Whoever made his own rtv moulds yet knows even the more affordable rtv silicone isn't that cheap - and you probably don't want to save money in the wrong place by using cheap silicone. Apart from that, some silcones aren't appropriate for spin casting, if that's what you're searching for.
I'm always keen experimenting and had a few minor accidents using an alternative curing agent.
The resulting moulds aren't satisying at all and there's no use for them, so I figured I could recycle them.
The first thing to do was apply a layer of silicone to the greens and plasticine.
Next, I sprinkled the mould with an equal amount of cured mould-pellets, it's kind of baking a cake.
After a day of curing the last layer is applied, silicone:sand - 1:1 (not any sand, fine quartz sand. I've tried other sand (even with additional curing agent), the results were fine but the curing still took a few days, it's not worth the risk).
This last layer provides an even surface and additional weight.
Cheers fellow cheapskates, let's see how this turns out :)