Struggling With Silk

I have 4 stamps that I am unsure whether or not are silk. The first two I found in various lots I purchased off ebay. None of them were marked as silk and I'm am leaning that they are probably not, however the blue fibers on the back are giving me pause. I understand you may not be able to tell from the pics, but some of the more knowledgeable members here may be able to definitely say yes/no/maybe from the impression or paper type.

The last two stamps I purchased as silk from one of the more well known dealers from NY. I am really doubting the R20 is a silk. The R10 is a maybe. What do you think?

1. R67 - Of the 2, this is the one that I am most unsure about.







2. R54 - Since the date is a little early, it's likely not a silk, but it did have a descent blue thread. Not a good pic here, however. The strand looks much bluer on my computer.







3. R10 - There are a couple of stands on the front of the stamp as well, but they don't look that blue to me.








4. R20 - I really couldn't find any blue threads on this one at all. Certainly not in what was circled. Did find a red thread, however. These are the closest:

I'll take a shot at this! R67, correct color, cut cancel consistent with later usage, short fiber, I vote yes. R54de, paper looks too thin, fiber too long, I vote no. R54de is unlisted. R10 difficult to tell, I'll let others more experienced weigh in. Red20 red thread is intriguing, but the other threads are a definite no.

While the R67 might be, the thread is much too small to say that it is a silk paper. The same with the R10. If one needs a 10x or 15x to even see it then it is too small. None of the others are silk.