Whitening a Family heirloom knitted white baby shawl

by Jill
(England)

My mother crocheted a beautiful white baby shawl when I had my baby 32 years ago.

My daughter is expecting my first grandchild and I would like to pass it on as a family heirloom.

it has been stored away safely, but it has yellowed with age. How can I get it white again? I'm not sure if it's pure wool or man made fibre? Thank you.