Identification of photomechanical plate

I have bought two silver plates which carry an image etched with
some kind of photomechanical process. They have been inked and then
cleaned as you would do to print any etching but the ink has been
let to dry in the plates, so that you can see the image perfectly.
The image is made of little dots which are quite irregular. I
suppose that the plates were made to be given to the client because
silver is too soft and expensive to be used as an engraving plate
and the composition of the images is not thought to be reversed in
the act of printing. Can anybody help me to identify the process
used to make them? Thank you in advance,

Marta Barandiaran
Conservation Lab
University of the Basque Country
Spain

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                  Conservation DistList Instance 12:46
                 Distributed: Monday, November 23, 1998
                       Message Id: cdl-12-46-013
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