I did a couple experiments last night with a bit of "pure" silver wire and a lump of "pure" tin. The "pure" tin made much darker marks on the paper. This could simply be the result of the tin being softer. I made a half hearted attempt to anneal the silver wire with a lighter but I'm not sure if I succeeded in making it "dead soft". I may take another shake at annealing the silver in a small jewler's furnace over the weekend.
Does anyone know the relative hardnesses of silver and tin when they are in their dead soft state?
I found the type and color of paper mattered a lot when determining how well the markings stood out. I was expecting the markings to show up best on black paper. That turned out not to be the case. The marks were more visible on white paper but that wasn't the best either. I found the marks to be most visible on lime green post it note paper.
It occurs to me that people do brass rubbings and that the principle of leaving metal deposits behind on paper is probably similar. Maybe a very soft kind of brass would also work? Probably worth checking.
I'm surprised no one else has commented on this thread. It seems like such an interesting diversion from the standard ball point/roller ball/fountain pen selection that most other pens use.
I just did a totally custom pencil with a 2mm graphite "lead" from the craft store.