This section is from the book "Manual Of Useful Information", by J. C Thomas. Also available from Amazon: Manual of useful Information.
Wash in warm soap-suds and rinse in water a very little blued; if the feather is white, then let the wind dry it. When the curl has come out by washing the feather or getting it damp, place a hot flat-iron so that you can hold the feather just above it while curling. Take a bone or silver knife, and draw the fibres of the feather between the thumb and the dull edge of the knife, taking not more than three fibers at a time, beginning at the point of the feather and curling one-half the other way. The hot iron makes the curl more durable. After a little practice one can make them look as well as new feathers. Or they can be curled by holding them over the stove or range, not near enough to burn; withdraw and shake out; then hold them over again, until they curl. When swansdown becomes soiled, it can be washed and look as well as new. Tack strips on a piece of muslin and wash in warm water with white soap, then rinse and hang in the wind to dry. Rip from the muslin, and rub carefully between the fingers to soften the leather.
 
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