The center looks like a tube implosion made on an open end tube. The nearly parallel lines can result from holding the tube in and elbow down position so that as the glass gathers it collapses into the tube. It looks like he didn't close the pattern on the back of the marble.
After the implosion is done drop in opal and constrict the tube around it. The whorl that you see is probably the result of the heavy solid implosion marble twisting as the glass between it and the rest of the tube is melted down around the opal.
He adds white to the back to hide the open implosion and then does the dot stacks. You can see where one layer has curled up a bit from the dots placed on the next layer up
Compare that to this
http://www.youtube.com/watch?v=qz7SR3OjvRE