Washing Antique silk
Firstly I would say never wash delicate fabric unless you really need to.
Antique fabrics almost always come with time marks and I see these as part of their charm and prefer to live with them rather than risk damaging the fabric.
If you really must wash silk and it is in good condition and not brittle, follow these instructions:
Hand wash in luke warm water with a tiny amount of non-biological washing liquid and gently wash gently taking care not to rub the fabric too hard.
Rinse thoroughly in luke warm/tepid clean water again being very careful not to damage the delicate fabric.
Once washed hang it out to dry, I prefer to line dry on a coat hanger wherever possible, I use a cat hanger so I don't make marks with pegs or damage the fabric.