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I think the Pilkingtons aspect has been written up elsewhere (with Czech workers in the 1960s-1970s teaching local glassworkers the style, but no paperweights being produce 'formally' as a production item). However, there are some older, Czech examples around too in the UK, and no doubt elsewhere. There are stylised flowers as well as butterflies, and all tend to have less bright colours, and poorer glass with a slightly yellow rather than slightly (or sometimes quite distinct) blue-green tinge. I think it is not always easy to tell them apart.
Alan