The only way we can think to describe these is way cool! Working in much the same way as the Currier & Ives stereoviews of the past, these operate on the venerable principle of the stereopticon. The viewer does not use the 3D TV Glasses with one blue and one red lenses. These cards, instead have a nearly identical image for each lens - and of course, there is a cut-out for your nose. You can even adjust the focus - just squeeze the folded-out card.
There's a space for a short message and the whole card folds flat for mailing in the envelope provided. Perfect for the occasion when a gift is too much and a card too little!
Dutch artist Maurits Cornelis Escher (1898-1972) was and is one of the world's most famous graphic artists. The left-handed artist is best known for his impossible structures and amazing three-dimensional woodcuts and drawings. He was consistently fascinated with congruency, perspective and technique: often spending hours experimenting.
This black and white card is a reproduction of his famous Reptiles tessellation, originally created in 1943.