just making some glass
C & C are welcomed 
First off:
The caustics are nothing short of incredible, no “photon-spots” or
anything - great!
then again:
The object is suffering from lack of antialiasing in the refractional
highlights (jagged - visible - edges, often inside the raytraced object).
These are especially visible inside the black darkened areas.
/JoOngle
Not bad!
What J.O. says is probably due to too low Ray bounces, or depth. You might have it low. when multiple internal reflections goes beyond that limit result is black…
Stefano