Here is an ultra-cool CD 145 B insulator. There is a three-quarter inch flat chunk of metal in the dome with another over quarter-inch piece below it which appears to have broken off. And it is halfway embedded into an half-inch bubble. There are other much much smaller metal flecks and bubbles along with faint amber swirling. The collector I got this from had always believed the metal to be remnants of a bottlecap, and when looking at it thru magnifying glass, I seem to agree. It also will draw a magnet to the glass.