The backside of a frame tells us much about the history of the work.
Many of the paintings have a backside that is covered with a page of an old book.
The text usually has little to do with the work itself.
We noticed one exception. On this work (that depicts Mozart) a short explanation of the ivory painting techniques is given:

Normally the backside gives us a sticker with a handwritten number and the name of the person.
On a lower part of the sticker, a rubber stamp is placed with the text:
Elfenbein-Platte gemalt
(= Ivory miniature, painted on a sheet of ivory)

another example:

Italian miniature painting can show a paper with the French (!) royal lily.
They also may have a silk back, instead of a paper one. Often a fold-out support is integrated in the frame to keep it upright when placed on a desk.