Silicone from a caulking gun? Hmmm... I don't know if it would do it. I'm thinking it won't be wet enough to form a ball on it's own. I'm thinking of trying PVA & talc and as that will be a dry mixture, to wet it. Nah... when the water dries out, it'll be half the size and may possibly look cxxp.
Best all round if you use a resin/Araldite of some kind that sets and make them with that. Now I don't have any of that so was thinking of gloss enamel paint. That will set hard and be ball-able. But I'd bet that would be a long wait while it dries...