Soft edible diamonds

Has anyone out there used the soft edible diamonds and if so what did you do to make them shine., I bought some for my niece’s wedding but they don"t “sparkle” and when you put them on a white cake they look like a gummy dot. not pretty. Is there a trick I don"t know about? I tried painting the spot with silver and then putting the diamond on but ugh… Any Ideas or am I just out the money?