Please use easier words and easier expressins as possible when you speak to me.
I need dictionally haha.
I'm afriad that I don't understand what you mean exactlly.

But I think I understand what you mean.
It' very interesting idea.
I cann't deny and it makes sence for me also.
I don't know they carved or not.
They just looked "carving" for me.
But I think your idea is easier to understand this kind of beads.

Because 2 right beads in 2nd picture are between type 1) ans type 2) in fact.
When I touch the beads I can feel motif a little bit, and I can see
shallow cavity also.

So it means there are some qualities(not method) on bird beads, right?

Can I say following"?.

type 1) - Low quality beads(beads in 1st picture) -
white motifs are rised on surface.
If you touch the bead ,you feel the motifs.
And after white motifs has gone out,surface is almost flat.
White motifs are not fused well into thier body.
type 1) exist much more than type 2) ans type 3)

type 2) - Midium quality beads(2 right beads in 2nd picture) -
white motifs are rised on surface a litte bit.
If you touch the bead ,you feel the motifs a little bit.
And after white motifs has gone out,you can see the same shape of shallow cavity(?) as motif.
White motifs are fused into thier body in shallow.

type 3)- high quality beads(2 leftt beads in 2nd picture) -

White motifs are not rised on surface.
If you touch the bead ,you don't feel the motifs (surface is smooth).
And after white motifs has gone out,you can see the same shape of cavity(?) as motif.
White motifs are fused into thier body completely.
It looks like carving and filled with white material as a result.
type 3) is difficult to find compared to type 1) and type 2).

How about this classification of thier quality ?
So your bead in picture belong to type 3) also.

And How about the white material?
Do you think white material on type 1) is deffernt from others?

Oh! Every beads were collected by myself in east Java.
Every year I go to Java for hunting antiques.

The picture is the bronze bird found in same area as bird beads(Manik Brung).
And People there belive the bronze bird belong to same era as bird beads.

SHINJI