Surface prep needed for large glass object?

Hello all,

The project I have in mind is a very big glass
bowl, not as thick as a fish bowl, but definitely
big enough. Initially, I thought about slapping colored
glass onto the glass with silicone, then grouting
it, but I thought I'd better check with the experts
first.

Is there any prep necessary for the glass bowl
to accept the silicone and the grout? Forgive me
if this is a dumb question, but I could just fathom
the grout sliding right off the glass.

Keep in mind that I want the glass pieces; which
are frosted, to allow light to glow, so I can't
cover the glass with sand or anything.

Many thanks for your assistance!

Karen Marie