from a quick google search..not sure if it really explains it, and an excerpt from another search..
http://www.ffplm.it/w%20elenco%20processi%20foto.htm

http://sharlot.org/archives/photogra...section_5.html

and:
>I recently found an old print in a antique (junk) shop. It measures approx
>2.5 inches x 3.5 inches. It appears to be a ferrotype on paper. The reverse
>is a "post card" type back. In the upper right where the stamp would go, it
>says: "Mandel's Positive Process-No Negatives" there is also a line drawing
>of what I assume to be the process camera. It looks like an old lantern
>slide projector. At the bottom it says: "Copyright 1911 By The Chicago
>Ferrotype Company". All of this text appears to have been applied with a
>rubber stamp after )I assume) the print was made. The paper is
>approximately the weight of modern double weight silver paper. The image is
>that of an average family sitting on a porch (a snapshot) so it's not like
>it was a commercial postcard of the Grand Canyon or something.
>
>Two photo historians at the local university looked at it, one specializes
>in non-silver processes and the other in 19th century photography, neither
>of them had seen one before or had heard of the process. Both did agree
>that it appears to be a 'paper' tin-type.

Tell them to check Melanograph and Monobath processes in my Encyclopedia
for a clue. They are fairly common.

I don't have my databases at hand but I am about 99% sure that this was a
direct reversal print, popular early this century with itinerant
photographers. It may also refer to the type of camera specifically used
for it. I'll check tomorrow.

Luis Nadeau
nadeaul@nbnet.nb.ca
Fredericton, New Brunswick, Canada

http://www.usask.ca/lists/alt-photo-...t96b/2486.html