How do I get the yellow out of white satin?

Hi Linda, here's an article that may help you, however, I don't know where to purchase the Vintage Tile Soak it mentions. Perhaps google that to locate a store or perhaps Amazon carries it. Hope this helps you restore the satin dress.

http://www.howtocleanstuff.net/how-to-remove-yellowing-from-old-satin/

You could try soaking it in oxiclean.

I know people who deal with antique linens, and from what I've heard oxi-clean and drying the item in the sun work well. However, any treatment could potentially damage the fabric, so you may want to test it out if you have a scrap of fabric from the dress or an item of a similar age and fabric.

Hi Linda! I was able to get stains out of a very frail 60 year old christening gown by making a paste of powdered OxyClean and regular hydrogen peroxide. Dip the stained part into the peroxide and then sprinkle the Oxy powder onto that area and then sprinkle more peroxide onto that. Then just let it sit overnight. The next morning get an old toothbrush and GENTLY scrub the area and rinse under clear cold water. Check to see if the entire stain has been removed and if not, repeat. Once the stain is gone soak the entire gown in a tub of OxyClean and lukewarm water. Don’t scrub or wring just gently slosh it around in the tub. Rinse well and hang to dry. Check again before completely dry to make sure the whole garment is clean and repeat the soak/rinse if necessary. Good luck!