Mix the Oxy powder with warm water in a bucker or sink. Soak the shirts for a day or two (or longer). It will eventually come out. I've done this with some very yellowed curtains and once got a red wine stain out of a brand new shirt of DH's this way. I had to soak the shirt for like 3 or 4 days (I think I changed the water/oxy solution once) but it came out eventually. good luck
Re: White shirts that have yellowed. Help!
Mix the Oxy powder with warm water in a bucker or sink. Soak the shirts for a day or two (or longer). It will eventually come out. I've done this with some very yellowed curtains and once got a red wine stain out of a brand new shirt of DH's this way. I had to soak the shirt for like 3 or 4 days (I think I changed the water/oxy solution once) but it came out eventually. good luck