Tinted glass plate negatives

Deborah Tint <dtint [at] verizon__net> writes

>I am scanning a set of 8x10 dry plate glass negatives dating from
>1910-1937.  We are scanning them to create positive digital
>"prints". In some cases the whole plate or selected areas have been
>painted on the emulsion side with a transparent deep magenta
>material.  ...

Photography has long been replaced by digital scanning for graphic
arts, but in the eighties, many older print shops still had large
format "process cameras" lurking, unwanted and abandoned, in dusty
corners. I suspect the plates in question were meant to be used in
the graphic arts / printing process. Large format films and plates
were common--I was renting 4 X 5 inch cameras to produce images for
reproduction thirty years ago--smaller formats were not acceptable
(not for fine work, anyway).  Only a portrait studio or a print shop
would be using 8 X 10 format.

In graphic arts work, red or orange adhesive film, dye, or paint was
used to "block out" areas on positive and negative transparencies.
Most commonly used darkroom films are not sensitive to red light, so
these areas would have been "blank" when the transparency was used
for creating the next step of the process. The block out material
would have been applied to the emulsion side, else there would be
bleeding and shadows at the edges upon projection or contact
printing.

Presuming the images are meant for reproduction, it is very likely
that they were purposefully developed to form a low contrast image.
The combination of dot "screens", printing methods, and papers
commonly used in offset and other printing methods would have
substantial effect on the contrast of the printed image (almost
always increasing the contrast). A good graphic arts department
would provide images with an appropriate tonal range (with attention
to detail in the highlights and shadows). I think a soft tonal range
is even more important for gravure printing.

Working directly on films and plates was a common procedure right up
to the death of the film-based graphic arts industry.  I remember
walking through a large room where images on film were being spot
bleached with wads of wet cotton and a lot of skill (to reduce dot
size and lighten highlights).  This knowledge is quite antique now,
but I'm sure an old (and he would be old, now) graphic arts hand can
provide you with a more comprehensive and accurate explanation. This
would help you electronically adjust your contrast when you print or
display the images from your plates.

Jerry Shiner
Keepsafe Microclimate Systems
+1 800 683 4696


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                  Conservation DistList Instance 25:46
                  Distributed: Sunday, April 15, 2012
                       Message Id: cdl-25-46-002
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