I'm new to this, but I've done my studying and research. I see a washington 15 cent perforated 12 with a double line watermark( a backward S), on bluish paper. Surely it couldn't be a (382 printed 1911 with a single line watermark) because of the 1910 cancel?
For whatever reason when I put the stamp in watermark fluid the very first time the water was extremely strong, it stood out and was very distinguishable. But since then its been harder to see, I've placed an order for another brand to see if it makes a difference. It was just recently that I ran into info stating that the watermarks show very strong on the bluish paper stamps. Its one of the main reasons I was convinced it was indeed a 366. Then again I'm puzzled by not getting the same results trying yo get that watermark to pop.