When the particle-containing surface zone of the layer (L) is thicker than 50 ??m, or in particular even 20 ??m, measured from the surface of the layer (L), which is in general the case when the abrasive particles are uniformly distributed throughout the layer (L), it is advantageous, as mentioned above, or may even be necessary, to employ abrasive particles which are permeable to actinic light, a