Harvard Natural Sciences demo: striking a rusty iron ball against an aluminum-foil-wrapped rusty ball triggers a safe, repeatable microscale thermite reaction with visible sparks.
Mechanical impact from two ~2 kg, 7 cm iron balls provides the activation energy; no external ignition source needed.
Yellow sparks are microscopic molten iron ejected into air, re-oxidizing on contact and emitting light via electron excitation.
Once initiated, the reaction is self-sustaining and oxygen-independent, the same property exploited in railroad track welding and underwater welding.
Setup is reusable: re-rust balls in salt water, replace single-layer aluminum foil when perforated, rotate contact surfaces between strikes.
Hacker News Comment Review
Discussion is lighthearted with no substantive technical debate; commenters focus on the accessibility angle, noting pétanque balls as a realistic household source of rusty iron balls in some regions.
