Are you asking about this type of bead?
The way I do it is:
1) Make a little tube that's just about 1-2mm narrower than your lentil press.
2) Encase it with clear thinnly.
3) Build up the sides of the lentil by adding glass only on the two sides - use your lentil mold to guide how you add glass - put it in the mold without pressing and help ooze it a bit into place while it's hot. Don't melt the core.
4) Once you've got the right amount of glass in a rough lentil shape, heat it well and give it your final press.
~Juliet