Oil Slick has become kind of the DiamondCast™ signature blank. They have definitely set the bar on this colour mix with a pouring method that all but guarantees you get all 6 colours, even on smaller pens.
These are best drilled on the lathe and for best results paint the inside of the blank. Use white paint for brighter rainbow look and black paint for more of an oil slick look.
DiamondCast™ blanks are indivudally cast using Alumilite and contain real diamonds for amazing sparkle and depth. Size is approximately 20mm x 150mm.