Marble effect pigment for injection molding

The marbling effect or tortoise shell effect developed in the last century was typically achieved by adding 2 or more different colors of the same basic resin and processing through a plunger style machine versus a reciprocating screw machine as is commonly found today. The reason it worked was because that type of injection molding machine did not mix the materials very well and you would have streaks of the dissimilar colors showing on the surface of the product. A similar effect can be achieved by removing a section of flight from the mixing section of a general purpose screw for a reciprocating screw injection machine. To my knowledge, there has never been a true "Marble Effect Pigment" that gives the effect every time with any type of equipment.

Can it be done with standard Injection molding grade soft PU resin? How to select pigment component to create partial melting in final part. Also can it be minimized for not to come to surface and stay inside part

- - - -> by: DG