Someone asked me how these are done - I don't believe it's a big secret - but I couldn't find the reference.
Make a bead in a light ivory glass - I used either Moretti or Vetrofond - not sure which. Make and shape your bead.
Take some very thin Fine Silver wire. I use 30 gauge, you could use slightly heavier gauge. Fine silver is 99.9% silver. Sterling silver will not work.
Spot heat one place - I choose a spot at the left side of the bead. Heat that spot to soft, and take it out of the flame and press the wire onto it. Hold the wire well back from the bead, and do not put it in the flame.
Still out of the flame, spin the bead, keeping tension on the wire, and guiding. If you have a bead with very steep sides - you may have trouble getting it to stay and not slide - so I tend to apply this to beads with more gradual slopes. I usually wind down to the right end and then back to the left, where I started.
I use about 10 inches for a bead - I have a spool of the wire and just use it off the spool.
Go back to the flame and flame-cut the wire at the bead.
Now go back into the flame and melt the silver.
The silver will break up into little balls, and it will also react with the ivory, creating the dark, streaky trails.
You may find that the place where you spot heated to attach the wire has distorted, so heat and fix that area.
For these beads, after they came out of the kiln, I cleaned them and then etched them. I use a liquid etching solution, and because mine is fairly fresh, these were etched for about 10 seconds. It is just enough to take the gloss off, without a rough texture.
(The etching solution is poured back into the bottle after use. Please make the effort to read the microscopically-tiny-print instructions on the bottle. You can use the glass etching solution found at craft stores and stained glass stores. Never pour acid in a manner that will make it splash. Use containers that will not but re-used for food. Acid can burn you - use rubber gloves, and remember, an acid burn can feel like an itch at first - not like a heat burn. )