How to Make Invisible Ink for Your Printer

Ok, user beware. This project, How to Make an Invisible Ink Printer, featured in the MAKE Blog, sounds like a blast; but it does involve cutting open an inkjet cartridge, removing its insides, and replacing its ink with lemon juice. I'm sure that printer manufacturers would strongly urge you not to try this, and if you do, the responsibility for the consequences are yours alone. But if you have an old printer that you don't mind experimenting with, and if you're handy with tools, let me and the rest of the About.com readers know the results of your experiment with invisible-ink printing!