platinum (n.)

metallic element, 1812, Modern Latin, altered from earlier platina, from Spanish platina "platinum," diminutive of plata "silver," from Old French plate or Old Provençal plata "sheet of metal" (see plate (n.)). Related: Platiniferous.

The metal looks like silver, and the Spaniards at first thought it an inferior sort of silver, hence the name platina. It was first obtained from Spanish colonies in Mexico and Colombia, brought to Europe in 1735, and identified as an element 1741. Taken into English as platina (1750), it took its modern form (with element ending -ium) in 1812, at the time the names of elements were being regularized.

As a grayish-white color (similar to that of the metal) it is attested by 1923; especially as a shade of blond hair, it is attested by 1927 (in platinum blonde "woman with platinum-blonde hair;" Jean Harlow, famously associated with the label, starred in a popular movie of that name in 1931).

There is a blonde type to me more irresistibly lovely than all the rest of the women who come under the "preferred" classification. She is the platinum blonde. ... There are thousands of blondes with gold in their hair, and as many with red, and quite as many again with the yellow of corn, some real and sometimes corned with the aid of a well known bleaching ingredient—but the platinum blonde maintains her supremacy by her rarity. [Antoinette Donnelly, beauty advice column in New York "Daily News," Jan. 25, 1927]

 As a designation for a recording that has sold at least one million copies, platinum is attested from 1960 ("The Battle of New Orleans"); in the late '50s it had been used to commemorate 3 million sales of a record (Pat Boone "Love Letters in the Sand"), and, from 1954, 25 million in total record sales (Jo Stafford, Gene Autry).