You write, "I do not know what causes transparent amber to darken and turn more opaque...."

My point was that transparent amber DOES NOT become opaque. It merely darkens. When it's held to the light it will be seen to have remained transparent (minus the degree to which it has darkened). There is a distinct and significant difference between dark amber and opaque amber.

Next, you write, "...the largest bead in Carl's strand would be a typical one...."

No, I cannot agree. The large bead in Carl's strand is probably an old specimen of native copal. As "amber" goes in west Africa, actual amber is much more common than copal (except in recent beads from less than about ten years ago). The copal cannot be called "typical." However, it's look is specific to these beads. This material ages differently (and more radically) than amber. To compare it to amber is a mistake. What has happened to this bead is similar to what happens to amber NODULES after thousands of years. I have already said that opaque amber can be made more transparent with treatments (that include heating and oil). However, these copal beads are most likely MADE from translucent material. So, of course, oiling them will return them to this appearance (somewhat)—because they were not opaque.

Next, "Amber initially opaque will turn of a richer shade, but will not gain translucence, no matter how much we massage it!"

This is absolutely mistaken. It is routine to clarify opaque amber, for over 120 years that recorded history tells us, and probably much longer. It is true that this is a factory practice, and not something individuals do (easily). But the simple fact is that clarifying amber in oil is a tried-and-true proceedure. "Massage" has nothing to do with it.

Next, "I guess there are two types of opacity: one that is congenital to the amber itself and due the impurities, etc. of the material, another one caused by aging (i.e. weathering** of the surface."

Absolutely not! The two types of opaque amber are those I described in my previous post. Aging does not precipitate opacity (except superficially, and in-appearance—as opposed to in-substance).

Finally, "...specially 'sanding', because I have only found this caracteristic weathered surface in beads from Northwest Africa (Sahara area), never for example in Tibetan beads."

By "sanding" are you referring to the highly compromised granular surface of the large bead Carl showed? This is a COPAL bead from Africa. It is not surprising you have not seen these beads from a Tibetan context. It would not be impossible, but it would be unlikely.

Jamey