I've had success washing satin. But yes, you need to make sure the red won't bleed. You can dip the hem of the dress in tepid water and let it rest on a white towel for about 20 minutes to see if it bleeds. After satin has been washed I steam it while damp so the wrinkles don't set. If you would rather not risk the whole dress, you can spot treat the armpits. I use a paste of baking soda and hydrogen peroxide. Let it sit (its best to rinse and repeat rather than let it sit too long and have it lighten the fabric) a few minutes and rinse. Blot the wet areas with a towel and you can even blow dry to speed the drying process and make sure no color transfer happens. If you want to wash the whole dress and you have found it is colorfast, I would just use a mild detergent such as dawn dish soap or woolite. You can add some baking soda and hydrogen peroxide to the water to boost effectiveness of the dress is really dirty. Rinse, roll in towels and hang to dry. Again, blow dry the strip of satin just in case! I'm always happy to answer questions about washing vintage if you need more answers!
