Black patches in glass when using cycles render engine for some reason i am getting these black patches all around my image. it seems to be most obvious where certain sections overlap slightly, but i have no idea how to fix them (very new to blender o.o) 

im not sure why this is happening. heres a version where the points im referencing are circled



i don't know what settings you guys need to know so just ask me if you need too. i can tell you this was only renderd 10x but even at 20,000 samples it did not fix anything

keep in mind, i am still a noob at this so any suggestions please word as simplisticly as possible xD thank you!
This is caused by sharp, low poly geometry with smooth shading (you'll notice that the problem goes away with flat shading). It's true that bounces can also cause dark spots (as mentioned in the other answers), but I think this is the issue in your case.

There a couple things you can try:


Adding more geometry (works well for curved objects)

No subsurf:

Subsurf level 2:

Using an edge split modifier (works better on objects with sharp edges)

Without edge split:

With edge split: