I think Jamey was first to point out that black glass is almost never really black - instead, a deep magenta, green, purple, or blue.

Once upon a time I recollect viewing a strange black glass that under magnification appeared to be fine black dust distributed through a jelly-like gray matrix. Maybe if a miracle happens I can find that bead again. Meantime...

This is a question for glass workers and chemists - what, if anything, actually produces black in glass? Evidently some of the late 19th century Japanese enamellists working with German glass chemist Gottfried Wagener discovered that uranium in a reducing atmosphere will produce a transparent (!) black.

Anyone know anything about this?