Turn glass into gravel - PEM BB wastestreams.sand.gravel

This is a badge bit (BB) that is part of the PEM curriculum.  Completing this BB is part of getting the sand badge in Waste Streams.

Once at an ecovillage in New Zealand the elder had amended his steep gravel driveway with crushed glass bottles.  They weren't sharp enough to worry about and gave great traction for tires and shoes.  I didn't try barefoot but I think it would have been fine.  What an interesting way to avoid replenishing gravel by using used bottles.  Let's give that a shot!

Unsurprisingly there aren't many pictures or videos of this so you'll just have to figure it out on your own.

Minimum requirements:
  - Make a gallon of glass gravel
  - Pieces need to be smaller than 1/4"
  - Need to be tumbled or otherwise wore down so they are relatively dull

Provide proof of the following as pictures or video (<2 min):
  - Bottles you're starting with
  - Your gravel making system
  - Finished glass gravel showing at least a gallon of material
  - Close up showing it isn't sharp