Hi Geoff, that's pretty similar to my playing about with much smaller fluffy feathers as below.
1 split down stem/quill
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2 glue two halves together to bulk it out (could even do 3?)... there is a natural curve, so make sure they match
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3 a bit stuck here as I don't have a tricorn to play with, but my idea is to glue inside the brim then use a tacky glue/hairspray/varnish, whatever, to curve them over and hold in place. I'm going to try leaving them folded over overnight and see if they take up a curve
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4 then, as you say, trim
I got that furry fabric today: looks good (pic is just around the top of my finger: with today's screw tops there's a dearth of corks... so we'll have to pop a bottle tonight to get one
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I haven't trimmed it at all... it would need a haircut for smaller scales.
Only danger is that we're becoming a bit too much like those 'dress-em-up' action man figs (as with models, there's whole wardrobe fulls of German/SS uniforms... all rather worrying if you ask me).
https://www.monkeydepot.com/Boxed_Figures_s/73.htm