...but you can make silk yarn from a silk hankie:
That's one 1/2 ounce stack of silk hankies that I bought at Sock Summit and started spinning on the spot. Today I finished spinning and plying, washed it, and hung it up to dry with the spindle as a weight to help set the twist.
Out of that 1/2 ounce I got about 125 yards of what I think is about laceweight, though the thickness varies quite a bit. What doesn't show in this shot is the marled colors, since the original hanky was dyed pink and purple.
Knitty has a great tutorial on spinning silk hankies. The hankies and spindle I bought at Sock Summit came from Royal Hare. Woodland Woolworks carries 1 ounce hankies, both pre-dyed and undyed.
Now to figure out what to make from the fiber. I'm thinking it might be just enough for a lacy triangular scarf.