Knackstedt & Naether began most likely in 1898 publishing and printing stereo views in postcard size. Relatively few cards were postally used. A K+N stereo postcard showing a bridge at Geneve, Switzerland bears the card number 694 and was mailed to Brussels, Belgium in July 1899.
Cards for the inland market (German address side) usually show two D,R.G.M numbers imprinted. The abbreviation stood for Deutsches Reich Gebrauchsmuster Schutz. People could register new designs or makes for a certain period of time = it was protected The numbers read 83,768 and 92,395. The lower number was for design of a postcard with stereo views registered for Alexander Platowitsch on 22 November 1897. Platowitsch was a photographer from the German city Hann.-Muenden.
So either K+N had bought the registered design from the photographer or used it in license. However, it is a bit confusing to see several other DRGM registrations on the same subject. For example a Conrad Toepfer held DRGM number 84,777 for a postcard with two views to be used for stereo viewers. It was registered on 20 November 1897. And there were others. I guess there were only minor differences.
Stereo photos were known (and popular) since the 1850’s. By the late 1890’s the stereo cards became part of the general picture postcard boom.
All K+N stereo cards I have seen so far show an undivided address side = were printed before 1905. Guess the boom faded by then and K+N concentrated on the more profitable picture postcards. All their cards show individual numbers believed to be consecutive. In this case K+N published some 3,000 different views. Keeping in mind that many views were printed not only with a German, but Dutch, Belgian or French address side / captions, the total number could be much higher. Proven is also that K+N printed Swiss views on order for the French publisher ‘LL’.
Most K+N cards show views from various places world wide, then we have series with people, fairy tales, romance etc. Some series were hand-coloured but the majority comes along in monochrome collotype quality.