filigranoscope électrique

OBS: Filigranoscope: Petit godet à fond noir au fond duquel on place le timbre-poste verso vers le haut. On verse quelques gouttes de benzine sur le dos du timbre. Le filigrane apparaît.

CONT: An electric watermark detector is a little plastic box with a hinged lid. (...) When a stamp is inserted in a slot and a light is turned on, the watermark can be seen under the proper colour in the disc.