Re: Gum dichromate issue

Giovanni wrote:

> Has anybody used dye transfer technique in a darkroom?

I have.

> Can I say that this process is a cousin of gum dichromate print?

It depends on how distant a cousin you mean. I'd call them third cousins at
best. Dye transfer is based on the hardening of gelatin by certain organic
developing agents. You expose matrix film through its base so that the
most-exposed layers are against the base rather than at the emulsion
surface. In this, it is the opposite of gum, in order to facilitate a full
tonal range. Matrix film has a reasonably ordinary silver-gelatin emulsion
that is not pre-hardened during manufacture. It usually has orange or
yellow dye added to attenuate the actinic light and give a more pronounced
depth of exposure through the emulsion layer.

After exposure, you develop and fix the matrix film (non-hardening fixer)
in the normal way. The developer byproducts harden the gelatin in
proportion to the silver image. When you then wash it in warm water, the
soft, unexposed gelatin washes away (here is where DT is like gum), leaving
an image with a distinct relief (somewhat like a carbon print or
Woodburytype).

If you then soak the film in a suitable dye bath, it absorbs the dye
solution throughout the gelatin layer. Because the emulsion has a relief
image, at any point the dye content is proportional to the thickness of the
emulsion at that point (which, in turn, is proportional to the silver
content of the image at that point, which is proportional to the original
exposure).

Finally, you sandwich the matrix film to a final support, emulsion to
"emulsion" (the "emulsion" of the final support is a gelatin layer that
contains dye mordants, typically coated over a baryta layer). The dye
diffuses from the matrix film into the "emulsion" of the final support to
form the final print. The matrix film can be used to make anywhere from
20-200 prints, depending on how it is cared for and how critical you are
about the final prints.

Of course, if you are making a color print, you do this three times, one
each for C, Y, and M (four, if you are using a luminance [black] layer,
which I generally did). One of the primary virtues of DT is that you have
opportunities to adjust image density, contrast, color balance, and skew
(different color balance in highlights and shadows) at every step of the
process. (All these variables also make it one of the harder processes to
master.) The techniques you mentioned in your original message are a some
of the less subtle of these controls.)

Because the dyes used in DT do not have to be formed in place by the action
of color developers in a silver-gelatin emulsion, which is the case with
common color materials, they can be chosen for longevity and fade
resistance rather than ease of formation from the development of an exposed
silver-gelatin emulsion. Thus, DT prints are substantially more archival
than other color photo processes (although Cibachrome [now Ilfochrome] is
also pretty good in that regard).

BTW, DT is (was) not always used for color prints. I made many, many
beautiful black-and-white prints using the process in the '70s. One virtue
here was the ability to make several matrix films (one for the shadows, one
for the midtones, and one for the highlights, for example), then use the
controls to adjust the contrast and density of each region independently,
giving incredible control over the tonality of the final image. Although I
rarely did, one can also tweak the color of the dye used with each matrix
film to get all kinds of split-toning effects.

By "a concentrated wetting agent," Langford meant Kodak Photo-Flo straight
out of the bottle.

Best regards,

etienne
Received on Mon Aug 9 12:11:22 2004