A familiar but little-talked-about product in the jewelry manufacturing sector called bimetal—­referring to two metals bonded together, primarily sterling silver fused to either 18k or 22k gold—is poised for greater popularity in fine jewelry stores. As a good alternative to solid 18k gold, bimetal helps keep down costs; it’s much more durable compared to gold vermeil or plate; it’s got more value than sterling alone; and it’s versatile to boot.“Bimetal allows you to do bigger, showier pieces without the cost of all gold,” says Barbara Wasserstrom, co-owner of Stuart Benjamin & Co. in San Diego, who introduced the metal to clients at the beginning of the recession in 2008. “I had to make things more affordable.”Wasserstrom carries the work of Christine Mac­kellar, who makes 80 percent of her C.H. Mackellar line in bimetal sterling and 18k gold. What surprises the