Thank you so much for your very nuanced response, Will - and thank you too Shinji, Hans and Fred.
Will, there are so many threads here to follow. Greatly appreciated.
With regard to the bicone bead photos you have posted with your message - I've been trying to understand them for years as I use them in necklaces. I've read that they are Han period Chinese beads that were imported into Thailand and Indonesia. Is this true? Also, I've always felt that the Ban Chiang beads I've seen were a squatter, heavier shape than the bicones that come out of Indonesia - and wondered at the difference. It occurs to me that you might have something to say about these things.
Many thanks,
Linda