In my first college art class 2 years ago, I was introduced to scratchboard. Scratchboard is basically a black sheet of what appears to be card stock, but when you scratch it using a 'scratch knife', the black surface is scraped off and white shows through underneath. It's like inverted drawing without an eraser.
I had extra time in the class between projects, so I asked the instructor for another scratchboard to start a new project... but I never finished it and eventually forgot about it (heh). Over this winter break I couldn't fall asleep one night so I got up and began organizing all the junk in my room back home. Low and behold, I found that 2 year old unfinished scratchboard! So I sat up and finished it. Time well spent, I'd say! I didn't have a scratch knife at home, though, so I had to be resourceful. I found an old metal pen, took out the ink, and used the edge of the empty pen tip as my scratch tool. The resulting lines were less refined/precise, but it's alright. I like the idea of doing cityscapes on scratchboard (and Chicago is the best city in the whole world, objectively speaking) and I want to try again soon with the right tools!