The steel frames go through four stages: hand polishing, nickel-plating, electroplating and lacquering, which give them a unique feel.‎ Vegetable-tanned and tumbled Spanish bovine hides and skins: this traditional method of tanning hides and skins is a technique based on natural tannins obtained from vegetable barks or fabrics.‎ The tumbling process and the use of natural oils and fats give the leather a distinctive flexibility and texture that age well.‎ All hides are carefully selected, with a minimum thickness of 3.‎2 mm/13 in, using the rump part of the animal, which allows for larger, more uniform pieces.‎ Available leather colours are black, navy blue, dark brown, cognac and natural tobacco.‎