A much easier way to use magnesium is to buy it in shreds form from a chemical supplier. Over here in the UK it was about $10 for 250g ( about 8 or 9 ounces). Seal amounts in a plastic drinking straw as you do cotton wool balls. When you need it, tear the end off and pour out the contents, add a suitable preprepared tinder pile and you have fire. I've used it this way several times and it's a lot easier than scraping it off a bar and the heat generated has always started a fire. <img src="/images/graemlins/grin.gif" alt="" />