Thanks Nel! The Gierlowska booklet is informative and available on line for a modest price. I can't find the link to the order form at the moment - I'll post it when I find it. Some other sites have a lot of the same information (see link).

From what I have seen so far, most amber imitations try to mimic "jewelry grade" amber articles. I have actually been in touch with Dr. Gierlowska (Google translate to the rescue!) and she says most of the new, really fine imitations are made of epoxy resin now.