@ fishy girl. Im sure it takes a loooooong time. All of the drawn reef and fish are really small. As far as I understand, the artist has to draw those scenes into the back side of the clear glass. Then the clear glass magnifies it. Probably to took hours and hours of work.
@Mimzy. I don't know him personally but I own some of his pipe work. I have methods of contacting him which I will do in regards to some pieces like these but as far as I know he is backed up on orders for the next 3 months. So I'm gonna add myself to the waiting list. This is the only site that has all of his work on display but its mostly pipes:
http://www.glasspipes.org/Kennaroo