Chiming in as my first post here.
It is doubtful that they are true silk papers. The paper type looks like the early thin paper; it doesn't have the right color or consistency for a silk paper, in my opinion. Also, any supposed silk paper with a cancel date prior to mid-1870 should immediately be suspect. While some documents were in fact backdated for legal reasons, they are by far the exception rather than the rule.
I've seen far too many "silk papers" in dealer stocks that were either (1) pieces of something stuck to the back, or (2) bits of wood pulp/fiber rather than actual silk threads.
Also, as I found out the hard way, a blue thread does NOT automatically mean silk paper:
http://www.revenue-collector.com/pages/1670.htmlI find that a USB microscope is excellent for seeing whether a thread is truly woven into the stamp or simply stuck to the back (I linked the image rather than posted it because it is a huge image):
http://www.revenue-collector.com/st...rcloseup.jpg-Dan