[TX_kiwi]

False alarm. I broke a yellow and a white to see.

The contrasting stripes and dotted lines on a Soprano are actually the core material. The outer (colored) plastic and the inner core are molded to allow the core plastic to reach the surface to form the contrasting stripes.

When the chip broke, it was obvious that this inner core plastic (colored white on most colored Sopranos) is dense and more brittle. It fractured with a rough and jagged edge.

The outer colored plastic appears to be softer and more ductile and had a smoother fracture surface.

The inner plastic core has holes in it (just like a metal slug) to allow the outer plastic to key through it to make a strong bond. They would manufacture these by casting the inner first then placing that in the final mold and injecting the outer layer around it.

Since the inner plastic material is denser, then it blocks the light in the same way that a metal insert would.

I guess you could conclude that they are 'slugged', however not with metal.