I use plastilina, never dry, oil based clay. After I carve out all the details I want, I just mold it with smooth-on silicone. In this case, I used mold star 15.
As for the glyph, I dont like it there because if you look at reference pictures, its really a projected light and not actually carved into the grenade.
already have 3 grenades cast out. pics will come tomorrow.
Going to do a run of this so watch the classifieds for my thread.