(Doll Hair - Black Dolls)
Pedigree hard plastic dolls had "wigs" of black astrakhan. Over the
years the hair fades and becomes less dense.
Taking off the old fabric is a laborious job but applying new material can make a big difference to the look of a doll. I prefer astrakhan but can no longer find it. A reasonable substitute is "K6 Curly" fur from Craft Online