Identification of photomechanical plate

Marta Barandiaran <uppbalam [at] lgdx04__lg__ehu__es> writes

>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?

Often times when a photomechanical image is put on a a metal plate
to be etched, in the very black areas (or areas that would print
black), the dot pattern becomes too fine and when dropped in the
acid to be etched tiny dots float away. Having experienced this
myself the solution was to use some sort of aquatint method or
mezzotint method to make the area black again. This was usually done
after the first "bite" so you could see what areas to mask off for
the aquatint (and several methods include spray paint or the pine
rosin method). These methods of aquatint leave an irregular dot
pattern where as the mezzotint is more patterned. You will find this
to be true especially if you see a photo dot pattern in the gray
areas on the rest of the plate. Also, the negative may be a straight
line shot which means there is no dot pattern, It was a high
contrast black and white translation and the dark areas were all
filled in with aquatint. A local print facility at a college or fine
art print shop could look at this for you and also help you
identify.

Carol Crawford, Library of Congress

                                  ***
                  Conservation DistList Instance 12:49
                Distributed: Wednesday, December 2, 1998
                       Message Id: cdl-12-49-010
                                  ***