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It is a
SWAN 4500 Noodle Pen
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You get beautiful thick & thins with just a slight adjustment in pressure...looks kinda like a brush marker but it has a thin metal tongue on the end to get the very fine hairlines & rubber instead of felt - I believe they're made in England.
Watch it beautifully demonstrated here by azavalia1
http://www.youtube.com/watch?v=sJ8c2ZMsK8U
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