Finding verifiable 1st issue silk papers still on documents is a daunting proposition, as quite frequently you can only see the blue silk threads from the back of the stamp. Sure, you can sweat/steam the stamp from the document to check, and then replace it, but frankly I shy away from documents with stamps removed and replaced. I realize it is an accepted practice with covers, but I just don't like it when a stamp has been removed and replaced.
Finding examples with blue threads visible on the front of the stamp so the document doesn't have to be lifted is far more challenging.
So that's why I jumped on this document when Richard Friedberg offered it to me at Chicagopex. It's an example of the 5-cent Proprietary silk (R29d) on an 1872 affadavit, the added bonus being that it is an illegal usage, which fits nicely in my current area of focus.
I count a minimum of 3, possibly as many as 5 blue threads visible on the face of the stamp.