“It wouldn’t have been called moon manicure because that was the default style,” said Suzanne E. Shapiro, the author of “Nails: The Story of the Modern Manicure.” The amplification of the lunula — the pale, crescent-shaped area at the base of the fingernail — created an elegant look that “made a well-groomed, almond-shaped nail appear longer,” as Ms. Shapiro put it.