At Bergdorf Goodman, I was treated to a glamorous chemistry lesson at the Prescriptives counter. Fully equipped to create or duplicate any shade, the Master Blender—a.k.a. the salesguy—examined my skin and lips carefully while peppering me with questions. Afterward, he squirted four different kinds of pinks and a dash of Bellini flavor into a mixing syringe. And in only five minutes, he had whipped up the “Kendall” gloss: a rich, medium rose that squeezed out slickly from a wand. I tossed my old lip gloss on the way out. 754 Fifth Ave., at 57th St.; 212-753-7300.