My dad used to use the bottom of a coffee cup sometimes. I have never tried it but I am sure it would work in a pinch.
Just make sure it's an unglazed portion. <img src="/ubbthreads/images/graemlins/wink.gif" alt="" /> You can also roll down your window in your car and used the top edge of the tempered glass to sharpen/strop your edge.
I don't think I will try this while driving down the freeway, cell phone in one hand, sharp knife in the other stroping it on my car window <img src="/ubbthreads/images/graemlins/eek.gif" alt="" /> might now end well <img src="/ubbthreads/images/graemlins/loopy.gif" alt="" />
