could they be drawn beads of some kind of satin glass including tiny stretched bubbles which have been dipped in a penetrating ink or stain, and the ends have gradually lost their intense colour?

there exist all sorts of embroidery beads coloured this way-

-just a thought.

The coin is a british colonial silver thrupenny bit- collectible in itself-

an interesting thought but I think these are too large for embroidery and they have the look of being very old and well worn. They were excavated and had soil in the perforations, I cleaned them. You're right about the ends losing their colour I was wondering if they had more than one layer. I learned something from your reply. I'm a Brit and have a small collection of silver threepenny coins.