Stereographs, in and of themselves, are not at all unusual. As recently as the mid 1930's and early 1940's they could be found in most homes here and abroad.
What makes this particular stereograph a standout is the fact that it is of the earliest type ever produced. Known as a "calotype stereograph", their survivability is quite rare. Predating the "Ambrotype", this process was after the daguerreotype. This stereograph is printed using the calotype process on very fragile paper medium, and then undercoated, or backed, with a fine tissue. The tissue, in most instances of this kind of stereograph is handpainted, and most of the "highlights" are pin-pricked to allow light to pass when held up for viewing, thus giving the highlight "realism".
The example does not show the handpainting, but rather, a sepia tone finish, which is always associated with "Calotypes". However, holding this 'graph up to the light, the pictures take on a whole new dimension. The entire scene, every item, is hand painted!
This particular style of stereographic "slides" were the forerunner to what became known later as common, paper-stock, cardboard-mounted stereographs, printed in the thousands. This style was originated in Europe, more specifically Britain and France, between the years of 1841-1851. The process was purchased by the Langenheim Brothers in 1849, and was brought to the United States where better lasting printing paper was used. "Rear painting", fell to disuse because the new papers were too opaque. This 'graph bears the inscription on the back: "Eglise Saint Paul Londres"
For more information on this subject, and further references, check out the publication: "Photography: The Early Years" by George Gilbert 1980, or "Photographs: A Collector's Guide" by Richard Blodgett 1979.
I found seventeen of these stereographs at an estate sale in 1982. They were intermingeled in a collection of over 600 of various ages and types, of stereographs. These, and a very few handpicked others, were my only acquisitions.
I will be posting others of this collection, at a later date.