This wonderful 1940s vintage gadget is 'The Philatector' Bakelite Electric Stamp Watermark Detector. It would have been the perfect accessory for the philatelist or bakelite collector providing a non-destructive method for viewing watermarks on highly prized stamps.

It has a series of colour filters which fit into a carousel, and a clear 'microscope type' slide. The stamp is inserted into the slide and the carousel turned so that the stamp aligns with a coloured filter. The switch is depressed to turn on the light so that the stamp can be viewed under the desired colour.

I do not know if the battery size is still available so being sold as a collectible for display only.