I believe that what you see is the white glass being way past its prime in the crucible at the time of manufacture. The white used in these beads is a fluorine opal which degrades over time in the pot. Over time it gets less and less opaque and hard white. Also fluorine opal at temperature is quite caustic to the furnace environment and dissolves the bricks and pots in the furnace. I've seen these beads before and think that all those white flecks are small pot stones in the glass.
just a glass makers opinion