Copper is a reactive metal and therefore the cooking utensils need to be lined/ layered on the inside to be food-safe. A thin layer of ‘raanga’ is coated inside the copper and brass utensils by extremely skilled artisans. This process is called ‘kalai’ and the craftsmen are called kalaiwaalas. This job of re-tinning the utensils needs to be repeated every six months or so because without the lining, copper may discolour the food, impart a bitter taste or sometimes, even lead to food poisoning. Jugs, glasses (products used for drinking water only) and decorative products don’t need kalai.