There are beads from W. Africa that are essentially brick-red over translucent green ("green-heart" beads), that have been abraded—and part or most of the red glass is removed.

Having seen a number of specimens, I suppoose some were made at Venice. I'm thinking of beads that are red on one side and green on the other, that do not appear to have been abraded. But many were African-altered—and these do appear abraded and somewhat clumsy.

I suppose your beads were African-altered, using a grinding wheel. When I was in Ghana in 1998 and 2005, the grinding wheels that were available to glassworkers were not devised to accomplish such work. They were rotary cranked wheels, made to hone blades. And they did not work efficiently on glass. The beads would snap-away from the wheels, and had to be repositioned. The smaller the beads are, the more difficult the work will be. Precision would not be expected.

JDA.