While studying minerals at the School of Mines, he believed he had found a new element. He announced this discovery in 1801 and suggested the name panchromium, meaning "all colors." The new element formed compounds of many beautiful colors. Del Rio later changed his mind and decided to call the element erythronium. The prefix erytho- means "red."
Del Río sent the mineral he was studying to colleagues in Europe for confirmation of his discovery. Unfortunately, they concluded that del Río's "new element" was chromium. Del Río's became discouraged and gave up his claim to the new element.