Yes, lovely dress! And I agree with Amy on the odor you get when you steam silk (wool, too).
Also, I find that with older fabrics, silk is much easier to discern than with more modern ones. On those, with enough practice and handling of different types of silk, you'll generally be able to tell just by the feel and sometimes the look (for example, the slubs in a shantung or a raw silk will be much more irregular than in a shantung-look synthetic). Today, high-quality woven polyesters can be hard to tell from contemporary run-of-the-mill silks, but generally not so when you're dealing with 60s & 70s silk vs. woven poly. While rayon and silk can, depending on the weave, feel and look very similar, and a burn test is the "best" way to tell if you're not sure, you often can tell by feel and texture (especially in conjunction with the "steam" odor test!).