The Palm Islands are artificial islands constructed from sand dredged from the bottom of the Persian Gulf by the Belgian company, Jan De Nul and the Dutch company, Van Oord. The sand is sprayed from the dredging ships, which are guided by a Global Positioning System, on to the required area. The process is known as rainbowing because of the rainbow-like arcs produced in the air when the sand is sprayed. The outer edge of each palm’s encircling crescent is a large rock breakwater. The breakwater of the Palm Jumeirah has over seven million tons of rock. Each rock was placed individually by a crane, signed off by a diver and given a Global Positioning System coordinate. The Jan De Nul Group started working on the Palm Jebel Ali in 2002 and had finished by the end of 2006. The reclamation project for the Palm Jebel Ali includes the creation of a four-kilometer-long peninsula, protected by a 200-meter-wide, seventeen-kilometer long circular breakwater. There are 210,000,000 cubic meters of rock, sand and limestone that were reclaimed (partly originating from the Jebel Ali entrance channel dredging work). There are approximately 10,000,000 cubic meters of rocks in the Slope Protection Works.