A lot of the vintage clothes we run into and sell are handmade...whether in a factory or by someone's loving mom. This is why vintage clothing tends to be of higher quality and why it lasts longer than today's "fast fashion" (and why Forever21 dresses will disintegrate after a couple wears). Anyway, because of superior production methods of the clothing of yore, there is not a lot of standardization in a) sizing, and b) labeling for care. We are here to help. Let's tackle washing your vintage pieces.
Listopad Rayon Colorblock Dress
Ah the conundrum of rayon. The first man-made fiber has a colorful history, including the drama of DuPont losing the original recipe in a fire in the '50s. You've probably picked up cool jersey shirts or draped dresses in a vintage store and thought for sure they were part silk or something else non-synthetic, only to find that it puts up with wear and tear better than silk or maybe there might be a little tag that says "100% Rayon or Viscose." Unfortunately, it doesn't tell you how to care for this fabric of the future. It feels way better than polyester, but does it hold up in the wash as well as poly? Not so much. Rayon does not deal well with water and looses elasticity/shape after washing so dry-cleaning is a must. If you are too cheap for that, though, the only thing I can recommend is spot cleaning with natural soap like Dr. Bronner's--don't soak or wet the entire garment, just dab a bit of detergent and water on the spots and try to soak it up with more dabbing of a sponge.
P.S. Modal is a heartier form of Rayon that can indeed be washed in the machine. It's made out of trees!