Need Help With A R28 - Is It Silk?

I'm having trouble deciding whether or not this is a true silk. It certainly looks like it has blue silk fibers, but I'm not sure about the paper type or impression. Please help!

Based on the paper color and type of the second image, I would say no, but color is very subjective. I would soak the pair and see if any of the silk threads disappear.

It would need a cert from the PF.

It is possible to have blue threads and it not be a "silk paper":

https://revenue-collector.com/pages/1670.html

i also have seen these fibers and would not call them silk paper. the size and shape are wrong. I believe that they were extraneous fibers in the "stuff" when the paper was made, and not added deliberately. the real threads are seldom more than an eighth inch long and often but one or two on a stamp and often appear to be in the paper under magnification. the first issue silk threads resemble the experimental silks of the match and medicines.

m and m - The first issue silks and the experimental silks on the match and medicine do more than resemble each other. They were the same batch of peper. The "experimental" was added in the catalog to differentiate it from the second paper variety silk paper. If I am not mistaken, the silk paper on the match and medicines are chronologically the third paper that was used for printing the private die stamps.

It was, but there was some overlap between papers at times. Only the BEP used only one paper, watermarked. Everyone else had at least some overlap.