In some instances, the best way to clean a vintage gown may be to soak it. There are some rules to be able to do this successfully. The best candidates for this are pieces of vintage trim, a section of a garment that can be removed and soaked on its own, or dresses that are only one layer of fabric (no linings or crinoline). The fabric that you are cleaning has to be able to be fully submerged and fit loosely into the water so it is cleaned evenly

I’ve had great results with CMDesigns’ Vintage Textile Soak and 7th Generation’s Liquid Dish Soap. The Textile Soak does a great job erasing stains from silk and pulling the yellow tint out of what-should-be-white vintage textiles. For tougher stains, like around a hemline, I work the dish soap into the stain with a toothbrush.

You can do this in a plastic dishpan or your bath tub. For a dishpan, I use ½ tablespoon VTSoak, for a bathtub filled to 3” deep, I use about 2 tablespoons.
1) Fill your pan or tub with lukewarm water straight out of the tap – deep enough to submerge your textile.
2) Add your VTSoak and stir it with a plastic or wooden spoon until it’s fully dissolved.
3) Ignore your sweaty palms and drop your entire garment into the water, using the spoon to agitate the water around the fabric.
4) The Textile Soak works so fast you can see the water change to yellow with 5-10 minutes!
5) As soon as you are happy with how it looks, drain out the water and fully rinse the textile with warm water. If the water gets too dirty, keep changing out the water and repeating the process until it you’re satisfied. I’ve also let a dress soak for two days before rinsing.
6) Lay it flat on a towel to dry