Abstract: The method comprises the production of a first positive model of an item to be cast. The positive model is produced with a flange extending in an imaginary separation line of the item. The flange extends both inwardly in the item within an outer periphery of the item and outwardly outside the outer periphery of the item. The flange establishes an artificial increase of the thickness of the item. Through different intermediate steps at least a first mould part and a second mould part of a mould are produced. The first and the second mould part of the mould initially have a separation zone forming a contact surface between the first and the second mould part. The mould parts are treated in the separation zone so that the negative moulds of an upper and a lower surface of the part of the flange extending outside the item will subsequently form a contact surface of the first and the second mould part.