I have talked about these beads quite a lot.

There is no real proof related to where they are from, nor what their timeline may be. However, they are recovered in Holland—so it's a reasonable guess they may have been made there. Because they are furnace-wound beads, there is no historical "factory waste" that could be recovered archaeologically. These, and pentagon ("twisted square") beads are placed in the early 18th C. as a matter of convenient speculation. I have no reason to suspect this is incorrect. Plus, the places where any of these beads have gone are sometimes noteworthy for having had known trade relations with Holland.

Apart from the van der Sleen Collection, the Archaeological Centre in Amsterdam has specimens of these beads. They told me none were dated, but that this suggested the beads were late. (Meaning ca. the 18th C.) The glass that was used has a severe tendency to break-down—indicting the the constituents were combined in a disadvantageous proportion. The outcome is, the glass decays easily (via leeching of the lime), and the beads OFTEN look much older than they are. The beads are routinely clear/colorless, white, translucent cobalt blue (from pale to dark), translucent yellow (sometimes modulated to an almost reddish tone, but mostly resembling amber), and violet.

When recovered in a Middle Eastern/Asian context, these beads are routinely mistaken to be and sold as "ancient."

Jamey