Trapped Bubbles. Discontinuities, actually flattened
bubbles in the filling, were noted in many of
the filled breaks with darkfield, oblique or pinpoint
fiber-optic, or overhead illumination. Unlike
natural, unfilled breaks, which have a mirror-like
appearance, these bubbles were always at least
partially surrounded by filled areas that were
either transparent or "cloudy." With overhead
illumination, some trapped bubbles exhibited
bright interference colors, a thin-film effect similar
to that seen in some natural, partially healed
fractures. The trapped bubbles occurred in a great
variety of sizes and shapes, singly and in groups