http://seattlepi.nwsource.com/artandlife/apother_story.asp?category=1404&slug=Translucent%20Concrete

http://seattlepi.nwsource.com/artandlife/apother_story.asp?category=1404&slug=Translucent%20Concrete

I love this idea. Makes me wonder if you could acheive a similar
effect at home perhaps using glass marbles as the aggregate?