Warning: a binder in Portland told me my grain direction was wrong and I argued for 20 minutes
I brought a finished journal to a meetup in Portland and a guy flipped it open, ran his thumb down a page, and said the grain was running the wrong way on the text block. I told him it was fine, then he asked me to fan the pages and they flopped open like a wet noodle. Now I test every sheet by folding it both ways before I sew, so what's your go-to trick for spotting grain when the paper has no watermark?
Feel for you on that one, nobody wants to learn grain the hard way at a meetup. I do the fold test too, but when the paper is thin I just bend a corner between two fingers and see which way it fights back less, since grain runs along the easy fold. It takes ten seconds a sheet and saves you from getting schooled in front of strangers again.