it’s OK to wash your silk! i use some of my daughter’s baby shampoo in warm water and give them a good squeeze. try not to wring your garment too tightly. thread will break under enough pressure. rinse thoroughly and hang to dry in a warm place.
will the silk shrink? yes, a little. not enough to make a difference in fit. at least with the modaspia styles which tend toward a loose fit. silk is wonderful in dry heat. it was nearly 95 f. here today and i spent most of the day in a bathing suit with the japanese spray paint print dress over it. the wonderful thing about silk is that it holds up so well over time. it’s one of the reasons you can still find beautiful silk garments in a thrift shop that are 40+ years old. my philosophy is if you have a pretty dress you like, don’t be too precious about it. where it whenever you like.