Wool, 14 karat gold
First things first: the traditional present for the sixth anniversary is NOT wool. It's iron. But for some reason, I had it in my head for a whole year that it was wool and I didn't check before making my wife's anniversary present. So, this year we're out of turn—next year we'll come back and do iron; and for our eighth anniversary we'll be back on track with the correct gift for the correct year.
I originally came up with this idea for our second anniversary, until I figured out that you can't make felt out of cotton—you can only felt animal fibers. Perhaps the fact that I've been planning this for so long is why I jumped the gun... no matter. I loved the idea of a really light felt depicting the lace structure of the capillaries of a leaf, after the flesh had decayed; and the more substantial main veins of the leaf could be depicted in gold. I actually took the layers of wool and felted them around the gold, so the cloth was made with the gold vein structure embedded in it. Makes for a beautiful, textural, autumnal piece of jewelry for a November anniversary.