They are indeed Bohemian Prosser beads. They are made with a compound combined in the mixture so that when they are fired, the air bubbles create this effect. They are often called lava beads. Many Prosser beads, both the French and the Czech have their band ground down, often so that you can not see it any more at all.
I believe these specific beads are not made anymore today, but were still made in the 1980's and maybe a bit after that.

As I remember he had a very good run on the black ones...but the brown ones were very difficult to sell. (!)

"Lava beads" is a misleading name because there also exist black stone beads of a similar bubbly consistency- almost as lightweight as pumice stone, which are made from pieces of real natural mineral lava i suppose. i have examples somewhere-...?

by some years. "Michael's", a mass retailer of craft supplies here in the U.S. is where I first saw the current version of "lava" beads - which do indeed look lava-like. First they appeared in black, with a suggested gimmick of putting drops of essential oils onto the surface of the beads, so one could have scented beads. Most recent visit to "Michael's" I saw beads of the same material dyed in weird colors. I like the basic black ones, though.

Hello Floor,

I have read that wax pellets are mixed into the prepared glassy/ceramic compound, that, during the heating process, melt away. So these "bubbles" are actually cavities formed from the exit of the wax.

I also tend to think of "lava beads" as being something else. But perhaps the Czechs use this name too.

Jamey

I have seen small bits of what seems like copper inside some of the holes, which seemed to me to also contribute to the effect of the bubbles, but not sure how they were made. The wax pellets makes sense.
They have been called lava beads by the Czechs, but they obviously are not lava.
On the market, most beads that are actual lava are brown or black (sometimes coated in a wax). However, in the last five to ten years or so, I have also seen another material being sold as lava, but it is entirely manmade. It comes in a variety of colors. It is a little bit heavier than the actual lava beads, and the texture is more consistent.

Hello Floor,

I have seen old/antique ornaments that are reputed to be carved from solidified lava, that are of a much more pale and grayish or buff color. It was a very fine-grained material. And not something recent.

Offhand, I don't recall reading a description of the Czech glass beads that named them "lava." I cannot say this is a mistaken idea. But I also cannot know for what period of time they may have used this descriptive identifyer either.

My point, in the reply I posted, is that these concavities are not "bubbles."

Jamey

They are sort of a yellow-beige color, I think I got them at a thrift shop.

I'll try to post a pic tomorrow, if my wandering brain can remember that long....