I follow some great typographers on Instagram, for inspiration. I noticed that quite a few of them were using homemade 'Soda Can Pens' - made from aluminium cans.
I did a search for them online and found a handy PDF template that you could download and use to make your own, so I polished off a can of fizzy pop (no brand names!), and gave it a go. I used watered down acrylic paint, which gave quite a nice finish, drying thicker and darker in places, and the flow of the nib was quite good.
I think I am going to try and make a few more at different sizes and practice using them, as it can give a really nice scratchy, loose finish - which would work well combined with strong photography or clean illustrated lines.