Iridium was originally found as a contaminant (with the element osmium) in platinum, and it was from the solid remnants left when platinum was dissolved in a mix of sulphuric and hydrochloric acids that Tennant made his discovery of both elements.

Astatine was discovered by D. Corson and co-workers in 1940 by bombarding a bismuth target with alpha particles. The most stable isotope of this element has a half-life time of only 8.1 hours.