Asphalt inside the crank pulley.......

[94 RT/10 Black MAMBA]

While changing my oil last night I noticed that the crank pulley looks like it has asphalt lining the inside of it. At first I thought I picked up something from road debris but on further examination the substance looksuniform around the interior of the pulley. I wonder if this is something DC put in there to balance the pulley?

Anybody got a clue?