I tried this last year.. i used toothpaste to get the bottom shiny. the chocolate didn't work so well. the only thing i could get to light was a dark piece of shredded cotton cloth. anything that was white or light colored didn't catch. the PJ cotton balls wouldn't even smoke. i figured the white cotton was reflecting to much light and heat to burn. the black cotton cloth only took a few minutes to get it to smoke and burn. you really have to use it on a very sunny day any and focus all the little pinpricks of light into one beam. the sun reflects off the can and makes a small circle of lights you move the can until they come together as one beam and focus the beam on the cloth. i was amazed it worked!! i thought it was just an urban ledgend. if it dosen't work the bottom isn't shinny enough. it should have a mirror finish on it. took me two hours of rubbing and a few failed attemps at lighting the cloth to figure it out.

i did a search on making fire without matches and then tried to duplicate them all. still can't get a fire plow to work.