This is an excellent observation. The difference between a silver (s shape)
and carbon (straight line) curve will certainly cause a difference in the
final look of a carbro versus a carbon image if made from the same
negative. What I meant by "appropriate negatives," however, is that the
negative would be specifically developed with the process in mind. I guess
this was not made very clear in my original post.
When shooting film which I plan to print with silver, or to make carbros, I
over-expose my negatives to get all of the important detail out of the toe
of, and then develop with Pyro, which flattens out the other end of the
curve. When you make a carbro from this kind of negative its look tends to
approximate what you describe as "the homogenous range of tones" of the
carbon," though certainly it can not duplicate exactly the carbon look.
Sandy
>
>> With appropriate negatives the final result in carbon and carbro is
>> identical.
>
>This is surprizing as dichromate systems and silver halide systems have
>different
>characteristic curves, the dichromate curve beeing more straight and the
>silver
>curve having the typical s-shape. With carbro, the image forms according
>to the
>content of silver in the silver bromide whereas in carbon the image is
>formed by
>the action of light according to the dichromate curve. This should lead to a
>somewhat more "homogenous" range of tones in the carbon transfer print. I
>haven't
>seen two identical carbon and carbo prints side by side yet, so this is
>just from
>theory...
>However I am quite sure that this homogenity of tones which I notice in
>old and
>new carbon transfer prints and for which I love carbon transfer so much is
>due to
>its characteristic curve.
>Klaus Pollmeier