It may not actually be blood. Quilt historians refer to it as age spots. Try Grandma's spot remover. Not sure I would use hydrogen peroxide on an antique quilt. Not sure I would even try anything else besides Grandma's spot remover. Contact a quilt historian. You can google it or try going to AQS website and find a quilt appraiser. Although you're not actually having it appraised, they are usually very knowledgeable on preservation also. You might also contact a local quilt guild. There are usually very knowledgeable people there also.