I found these extracts on 'The classroom @ The coop' Hope they may be helpful.
I think I would put them in the freezer for some days to be quite certain there weren't any "stowaways" (mite, lice etc).
I seem to remember my old mother telling of how they used to wash the feathers. They put them in a large pillow-case and sowed it shut. After washing in natural soap and rinsing thoroughly in luke warm water several times, it was important to shake the pillowcase while the feathers were drying to keep them from sticking together. The more - the better.
You will have to use down proof fabric (percale) and double small stitched sewing to keep the feathers/down in.
To fluff up the feathers/down after washing you can dry it in the tumble drier, cool, adding a few tennis balls.
As real down is too soft for a pillow and small feathers are kind of prickly, a good feather/down pillow should be made two-layered. One case just a little bit smaller filled with a feathers/down mix into another case with a layer of soft down between the two.
Sleeps like heaven! cool