I disagree. With magnesium block you can light fire even without very thin tinder (like lint or cotton balls). Just be patient, and spend more than 5 minutes shaving the magnesium in a very thin powder. The fine hacksaw blade is better than a knife in producing such a powder (and in producing the sparks too). Just use it as a mini saw. The magnesium pile must be something like 1/2 of teaspoon in volume at least (the more the better for an average beginner). Shave on a flat or better concave piece of more or less dry wood (paper, cloth). Spark right on the pile. Sooner or later magnesium will ignite. It will burn hot at least for a minute. Just add more fuel as usual, starting from a match thick kindling. Also watch the base piece of wood. It's usually develops a nice coal right under the pile.