We carried out some experiments recently lighting a length of magnesium ribbon with a Fresnel lens. The Fresnel lens was used to focus light rays from the sun on the magnesium. The magnesium ribbon acted as a fuse to ignite a thermite reaction mixture in which it was embedded. The experiments went rather well providing a relatively safe and unhurried way of starting this energetic reaction.
We used 20g of thermite mixture made from aluminium powder (5g) and iron (III) oxide (15g) which reacts according to the following equation:
Fe2O3 + 2 Al → 2 Fe + Al2O3
The experiments were carried out in the tropics and it would be interesting to see if the same method works in a more temperate clime.
Links to movies of the experiments on You Tube can be found here: