Most birds live outside and they do dust themselves. A few years ago I received a pheasant skin, and it was dull and 'sticky' to the touch. A quick slosh in a pail of tepid water with some shampoo made it shiny and manageable (what else would you expect - is this a new TV promo?) - rinse well and hang or lay out on newspaper to dry. The amount of grit in the bottom of the pail surprised me. This works well on road-kill squirrel tails too.

I have never felt the need to do the same with peacock herl, but I assume it would work just as well, and at least it wouldn't harm.