I've got a pretty good collection of postal cards from the 1873-1881 timeframe. I've been trying to determine the presence of watermarks using light at an angle, moving the card, etc. It's not happening. So, what kind of watermark fluid do you like to use? Or do you have a different technique I should try before buying watermark fluid? Thanks in advance,
Watermarks on US postal cards can be difficult to find. Oblique light is good and a strong back light can also help. You can try Ronsonol lighter fluid with the card on a black background. Daniel Bagby had a way of using photo paper under the card and exposing to light for a long term which would show eventually show whether or not there was a watermark. He would use it on UX4. Good luck.