Subject: How does extreme water pressure affect common materials?

I have been trying to understand what extreme water pressure, say at depths of 
6,000 feet or more, would do to everyday materials. Let's say I dropped a 
solid peice of plastic with no air pockets into the deep sea and it sank to 
the bottom (assume it is tied to a weight). What would happen to that plastic? 
Would it be compressed or crack? Or would the water pressure do nothing at all 
to it? Does water pressure only affect things with air pockets in them or can 
it do damage to solid materials also? I have been thinking of ways to develope 
a camera that would be able to explore extreme depths but I am not familiar 
with what our current limitations are or why there are limitations.
Thank you for any help.

Re: How does extreme water pressure affect common materials?