For centuries, a variety of techniques have been used to enhance the appearance of gems. The chart included with this issue describes gem treatments currently in the marketplace and indicates their detectability in specific gems. Shown here are some of the gem materials that may be subjected to treatment (and the fine colors that treaters try to duplicate). The cultured pearls range from 10.28 to 11.15 mm; the coral beads are 4.5 mm. The diamond (above the necklace) is 4.10 ct. The colored stones, left to right from the top, are: (row 1) 8.28 ct aquamarine, 10.76 ct tanzanite; (row 2) 5.77 ct yellow sapphire, 8.34 ct pink tourmaline, 10.99 ct blue zircon; (row 3) 8.56 ct pink sapphire, 8.37 ct blue sapphire, 5.56 ct emerald; (bottom row) 2.42 ct pinkish orange sapphire, 3.61 ct ruby. Cultured pearls courtesy of Kathryn Kimmel, GIA. Coral courtesy of Roben Hagobian, Glendale, California. Diamond courtesy of Norman Silverman and Louis P. Cvelbar, Los Angeles. Colored stones courtesy of Evan Caplan, Omi Gems, Los Angeles. Photo © GIA and Harold & Erica Van Pelt.