The Wild World Of Watermarks

One of the subjects I'd like to learn about is what is the deal with watermarks on the early 1870's postcards? I would say there are hundreds in this collection I've been touting here the last week or so. I do know that you can see the mark if you hold the card over a strong light. Some can be seen without a light, and I've posted three here where you can make out a mark. Hope you can see it. I also know some can be valuable and some not, but I have no idea what designates that outcome. Thanks as always for any help... Don

When you wade into watermarks, you are looking for a postal card specialist and not someone looking for cancels or advertising (ie. a different audience than what has previously been discussed).

"When you wade into watermarks, you are looking for a postal card specialist and not someone looking for cancels or advertising (ie. a different audience than what has previously been discussed)."

Well then....I am wading waste deep :) Is this the right thread then?

I don't know if you want to be in Back of Book or Covers.

"Back of Book or Covers."

Not sure.....new to all this.