Platinum was reserved for military use, so jewelers began relying heavily on gold and experimenting with colored alloys and different finishes. Retro jewelry designs are marked by asymmetry, motifs borrowed from industrial design, and exaggerated scale. Thanks to a hugely successful advertising campaign begun in the 1940s and funded by De Beers, the phrase “a diamond is forever” was coined and diamond rings were touted as the ONLY acceptable type of engagement ring. Carefully worded ads instructed men on how to choose a stone, and what to spend (“two months salary!”). The Gemological Institute of America developed the so-called “4Cs” of diamond grading, which was a scientific system for measuring the color, clarity, cut and carat weight of every single diamond. The costume jewelry industry, having only been established a few decades before, began to flourish. Centered in Providence, Rhode Island, and surrounding New England towns, companies like Trifari, Monet, Hobe, and Vendome prospered as consumers gobbled up inexpensive machine-made jewels.