Lanthanum and actinium: the two elements that give their names to the lanthanoid series and actinoid series which together form the f-block of the periodic table. The patterns I have chosen are representative of each series: the many applications of the lanthanoids and the radioactivity of the actinoids.
Lanthanum compounds have numerous uses, going back to the use of lanthanum oxide in gas mantles in the late 19th century. Nowadays lanthanum oxide is used as an additive in the optical glasses for camera lenses and telescopes as it increases the alkali resistance and the refractive index of the glass.
Actinium is a source of both alpha and beta rays, depending on the isotope, and naturally occurring actinium gives off a ghostly blue light as it excites the air around it. As it is scarce and highly radioactive it has few applications, though one isotope (225) is finding use in targeted alpha therapy to kill cancer cells.
Both of these patterns are inspired by the RSC’s Visual Elements Periodic Table, designed by Murray Robertson.