Old linens

Is there anything new out there for getting dark spots out of old (100yrs +) linens? Mostly sheets and pillow cases. Some had never even been used. Over the years I have tried Biz, lemon juice, sunlight, the horse soap (Orvus?) and, gasp, Clorox among other things. Still the spots remain. I am about to cut off the lace, etc. and use it for something else and toss the spotty parts.