Adverising Pocket Folding Stereoscopes (various)

wonderful collection of four German folding metal viewers, for cards 3x7cm, all in good original condition, (1,2) two identical viewers branded for the German weaving mill F.V. Grünfeld labelled 'Werdegang des Leinens in Wort und Bild' (the production of linen in words and pictures) with a series of 15 cards and a printed booklet in the original box, (3) box shaped viewer is made of painted and printed tinplate branded 'Kaiser's Kaffee Geschäft', (4) folding miniature viewer 'Cecilie' produced by the ‘Neue Photographische Gesellschaft AG, Berlin’, made of painted and printed tinplate, some matching cards.(4)