A method of manufacturing a primary mold for the forming of a retroreflective screen, the method including the steps of: a) forming, on the front surface of such a substrate, a layer of a material such that the first substrate is selectively etchable over said layer; and b) forming microrecesses from the rear surface of the first substrate by selective etching of the first substrate over said layer, each microrecess emerging on the rear surface of said layer and having a back parallel to the front surface of the first substrate and first and second lateral walls orthogonal to each other and orthogonal to the back the first and second lateral walls and the back of the microrecess joining at a same point and forming a trihedron.