Dufay Color processing (was really old film)
Richard Knoppow
I was originally going to post this material directly to Frank
Roberts but got some other e-mail expressing interest in this old
process so will post it.
I see there is already a post by Maxim Muir with processing
instructions. My material isn't much different but I will post it as
a matter of possible interest. I suspect there were a number of
variations in recommended processing over the years the process was
popular.
My two sources are _Handbook of Photography_ Keith Henney and
Beverly Dudley, 1939, Whittlesey House-The McGraw-Hill Book Co. and
_Color Photography for the Amateur_ Keith Henney, 1938, same
publisher.
First, Dufay Color was a film for making color transparencies which
was popular in the mid thirties. It consisted of a clear support
which was coated with a very thin layer of colodion. One this layer
was printed a cross-hatch pattern of colored stripes in such a way as
to have alternative squares of the three primary colors. This filter
layer was coated with the sensitive emulsion. The film was exposed
through the base and processed by the reversal method to produce a
positive transparency directly from the camera film. This could be
used for projection or, with some limitations, for making color
prints. There were a number of similar additive color films (e.g.
early Agfacolor, Lumier Autochrome, Finley Color) which differed
mostly in the way the filtering was done. All of these products were
killed off by Kodachrome and the later perfection of modern contained-
coupler negative and reversal subtractive color films.
A word about reversal film. Any emulsion can be reversed but for
best results the emulsion should be especially formulated for the
purpose. Reversal films have, in effect, two emulsions, although the
components are mixed together rather than being separate layers. All
emulsions contain a sensitive particles of varying sensitivity; some
require only a few photons to make them developable, some require a
lot. The contrast of a film is determined by the range and
distribution of these particles. For a film to work well as a
reversal film there must be a plentiful supply of low-sensitivty
particles. When the film is exposed in the camera it is mostly the
higher sensitivity particles which become developable leaving the
lower sensitivity particles avaiable to form the positive image later.
The film is first developed in a conventional negative developer.
The resulting silver image is then bleached out with a type of bleach
that removes the silver rather than converting it back to halide form
as Farmer's reducer would. After bleaching, there is left only the
undeveloped less sensitive particles. They are then exposed to a
strong light and developed in second developing bath which converts
virtually all into silver to make the positive image. Sometimes
reversal film is then fixed to remove any halide particles which have
somehow escaped being developed. The result is a high quality
positive image. The Dufay film was made by Ilford.
Here is the Dufay process as described in these books:
First Developer
Water 1000 ml
Metol 1 gm
Sodium sulfite, dessicated 50 gm
Hydroquinone 8 gm
Sodium Carbonate anhydrous 35 gm
Potassium bromide 5 gm
Potassium Thiocyanate 9 gm
Time of development may vary from 4 to 6 minutes at 68F, according to
the amount of exposure.
After a brief rince in water, lthe film is treated in a bleaching
bath:
Bleach
Water 1000 ml
Potassium bichromate 5 gm
Sulphuric Acid (sp gr 1.87) 10 ml
The bleaching will be completed in about 4 min.
Then wash about 2 min.
The film is then cleared in the following for about 2 minutes.
Clearing Bath
Sodium Bisulfite 25 gm
Water 1000 ml
After clearing wash again for 2 or 3 minutes or until all the yellow
bichromate stain is washed out.
Room lights can be turned on at this point.
The film is now re-exposed to white light, either diffused daylight
or a one minute exposure to a 100 watt incandescent lamp at 12"
distance can be used.
Then redevelop in:
Second Developer
Water 1000 ml
Metol 1 gm
Sodium sulfite 50 gm
Hydroquinone 5 gm
Sodium carbonate (anhydrous) 20 gm
Develop for about 4 minutes. Probably Dektol 1:2 would work as
well.
The film is now fixed for 5 minutes in a conventional fixing bath
and washed.
An alternative bleach using Potassium permanganate is given but
requires hardening in a Formandehyde bath. Both formaldehyde and
bichromate are nasty but I would rather deal with the bichromate.
The Thiocyanate in the first developer is a halide solvent which has
the effect of brightening the highlights in the final transparency.
Because of the intregal color filters I am wary of trying to process
the film as a negative.
As a note to the picky (I confess to being one sometimes) it is
possible to eliminate the second exposure by using a second developer
containing a strong fogging agent. Such developers are comonly used
in color reversal processes. It is also possible to develop in a
sulfide redeveloper as with sepia toning whic will develop without
exposure and result in a sepia image. Not a good idea for Dufay
color.
Good luck and please post the results to the group and to me via
e-mail. I am sure we are all anxious to know whats on that sixty year
old film:-)
---
Richard Knoppow
Los Angeles, Ca.
dick...@ix.netcom.com
Ron Speirs
Richard Knoppow <dick...@ix.netcom.com> wrote:
: I was originally going to post this material directly to Frank
: Roberts but got some other e-mail expressing interest in this old
: process so will post it.
: I see there is already a post by Maxim Muir with processing
: instructions. My material isn't much different but I will post it as
: a matter of possible interest. I suspect there were a number of
: variations in recommended processing over the years the process was
: popular.
: My two sources are _Handbook of Photography_ Keith Henney and
: Beverly Dudley, 1939, Whittlesey House-The McGraw-Hill Book Co. and
: _Color Photography for the Amateur_ Keith Henney, 1938, same
: publisher.
[Richard then describes Dufay Color and its processing formulas.]
Yes, these are the classic formulas for reverse-processing B&W film
to make positives. It is interesting to note that there is a current
film that uses the same theory and process: Polachrome by
Polaroid. It has microscopic stripes of red, green and blue, and a
B&W emulsion. The main difference is that Polaroid makes use of their
instant developing technology and provides a little pod of chemical
and a little crank device to instantly process the film.
Just as Richard mentioned that Dufay Color and similar films were
obsoleted by Kodachrome, Polachrome is NOT a viable substitute for
current slide films; its primary usefulness is where slides are needed
instantly, where and when conventional processing is not feasable.
Business charts and graphs are acceptable on Polachrome, but I don't
think many photographers would be happy with its pictorial results.
Just my opinion.
Ron Speirs