gild (v.)

"precious metal noted for its color, luster, malleability, and freedom from rust or tarnish," Old English gold, from Proto-Germanic *gulthan "gold" (source also of Old Saxon, Old Frisian, Old High German gold, German Gold, Middle Dutch gout, Dutch goud, Old Norse gull, Danish guld, Gothic gulþ), from PIE root *ghel- (2) "to shine," with derivatives denoting gold (the "bright" metal).

The root is the general Indo-European one for "gold," found in Germanic, Balto-Slavic (compare Old Church Slavonic zlato, Russian zoloto, "gold"), and Indo-Iranian. Finnish kulta is from German; Hungarian izlot is from Slavic. For Latin aurum see aureate. Greek khrysos probably is from Semitic.

From Homer on through Middle English, "red" often is given as a characteristic color of pure gold or objects made from it. This seems puzzling, but it might stem from an ancient practice of testing the purity of gold by heating it; in Middle English red gold was "pure gold" (c. 1200).

Nay, even more than this, the oftener gold is subjected to the action of fire, the more refined in quality it becomes; indeed, fire is one test of its goodness, as, when submitted to intense heat, gold ought to assume a similar colour, and turn red and igneous in appearance; a mode of testing which is known as "obrussa." [Pliny, "Natural History," 33.19]

1560s, past-participle adjective from gild (v.). Late Old English had gegylde; Middle English had gilden (adj.). In modern use the more dignified past participle of gild, alternative to gilt. Shakespeare's lilies were never gilded; the quote ("King John," iv.2) is, "To gild refined gold, to paint the lily." Gilded Age as an era in U.S. history (roughly 1870-1900) is from the novel "The Gilded Age" by Mark Twain and Charles Dudley Warner, published in 1873.