Some art pottery glazes are formulated deliberately for this effect. They are usually called crater or lava glazes. These beads look like an unusually active variety.
Here's an article with crater glaze photos from Ceramics Monthly. Sorry the photo is so large.
However, my gut tells me there is something not right with them. Genuinely old faience beads, erode differently, is my experience. The big air bubbles do not seem to fit faience. This many, looking this much alike, but different from (many) other faience melon beads makes me suspicous.
... it would be quite easy to fall for one of these beads on its own. But taken together, they're all too similar, and too obviously the product of some artificial "aging" process. What process, I wonder? And does anyone know where they are being produced?
As with many fakes, it's the greed of the seller - wanting to offload so many of them at the same time - that gives the game away.