Agreed with the Daguerreotype and tintype (which this is not). The ambrotype does not need to be backward unless the glass plate is put over the background backward exposing the emulsion to easy damage. However, I doubt that this is any of the above. The three named are extremely difficult to photograph from straight on due to the need for light reflecting at an angle off the surface (the ambrotype the least problem). I believe this is a paper print for the following reasons:

1. While photographers of the time did use wet plates, it is unlikely the glass plate would have survived this long in the condition shown as an ambrotype. Out of necessity, the plate would have been printed on paper for survival.
2. This appears to fall in the style of the Carte de Visite of the time which were printed on paper and often mounted on a heavy paper backing.
3. If this were an ambrotype (negative) the margins would normally be covered by a frame and, if they were not, would appear black rather than the white that is shown.

I believe this is a projection, paper print made from a larger glass plate. The glass plates of the time were considerably larger than the Carte de Visite they were used to produce (thus projection printed). It would take a very careless technician to not notice which side of the glass held the emulsion in making a contact print.