What type of silicone molding material are you using ?
Tin or Platinum catalysed ?
Tin cure silicones will cure against almost anything, including sulfer bearing clays like Roma Plastelina. Platinum cure silcones will be inhibited by sullfur, I use Protolina clay in my shop so
I’m good with any moldmaking rubber.
If you don’t know or the spec sheet for the silicone your using doesn’t say, then mix a tiny amount
and put a dollop of the mixed material on small area of the print and let it flow out and let cure overnight.
If the thin film cures then you’re good to go, if not then use a acrylic clear coat, it sprays on thin
and won’t fill in fine details, 2 - 3 light coats. I don’t know where you are in the world but in
US I use Krylon Crystal clear. Note this will give you glossy castings from your mold, castings are a
reflection of what the mold surface is , if you need matte then use a matte clear coating.