I remember reading on here once or twice that there's not really such a thing as black glass - just very dark colours which appear black until you shine a light behind them.
However, I recently bought a piece of 'Sort Palet' (Black Palette) by Michael Bang, and the colour does seem to be truly solidly black. The walls are only a few mm thick, and the inside is pure white, but the cased exterior remains a jet black - and it doesn't let any light through either (it's a mustard pot, and I slipped it over a 100w bulb for a few seconds - complete black-out). The lid is uncased, but equally impenetrable.
Will there have been a special process to have made the colour super-dense?Photo