The invention relates to a method for extracting, without using an organic solvent, squalene produced by fermenting microalgae belonging to the Thraustochytriales sp. This heat treatment can lead to deformation of the color selection electrode, because in color display tubes with an invar shadow mask, the diaphragm parts are made from invar as well, while the corner sections are made from iron in order to obtain enough stiffness. A patterned mask layer having a plurality of first features with a first pitch P1 is formed on the second material layer.