I recently purchased a bare conductive pen, was very disappointed. The ink was really thick and difficult to handle, I managed to find these guys who I saw at a UK maker fair, https://sites.google.com/site/thinkinkfactory123 the ink from these guys is sooooo much better, easy to handle as it is like a paint, they use some special Sri Lankan graphite which makes it super conductive, I tested and got 2 ohms per square, I could not get 600 ohms per square from bare!