Höganäs developed a technique in which the raw tile is painted with a clay slip of the same material and then fired. It is overlaid with a glossy, transparent glaze before it is fired the final time. This gave a beautiful lustre or sheen to the surface that would retain its visual qualities even when the tile became dirty. Over one million tiles were cast into precast concrete lids on the ground, and then bonded onto the ribbed superstructure of the shells