Black holes / Water in glass I try to render mineral water bottle filled with water in Cycles. For testing purposes I use super simple model with absolute flat lighting filled with white color.

What is bothering me are the black spots on the render. I mean, I know there should be some strange curves generated by IOR, but in the complete white environment black patches should`nt appear. 

What should I do, to avoid them? I`m attaching images with the render result.



I know that lighting and model are dull, but I use them to exclude any unnecesarry factors. My render settings are:





This is my latest bottle atempt with photo lighting. It looks better, but on the top of the bottle strange curves appeared. I think that it is caused by plastic rings on the bottle, but it look unnatural. I think that I`m missing something, because I still dont have control on this render behavior.
These "black spots" are actualy supposed to be there. 

Look at these images with similar dark spots



It is actually more prevalent in thicker objects so if you really don't like it, try making the glass thinner

This images has a glass with much thicker walls.