For glasses: Place sumac and sugar in a plastic bowl, wide enough to fit the rims of the margarita glasses. Rub each rim of the margarita glasses with a lime wedge or with lime juice. Then dip each glass into the bowl of sumac sugar to coat the rims. Set glasses aside.
Combine the cranberry juice, sumac syrup, tequila, lemon juice and 2 cupfuls of ice in a liquidiser/blender; blend until smooth.
Place 1 cupful ice cubes in a cocktail shaker/sealed container; add desired amount of margarita; cover and shake well; serve.
