PHOTOBLEACH PHOTOGRAPHY; EVALUATION OF FINAL REPORT PHASE II

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP78B04770A002800030036-1
• Release Decision: RIPPUB
• Original Classification: C
• Document Page Count: 32
• Document Creation Date: December 28, 2016
• Document Release Date: June 3, 2005
• Sequence Number: 36
• Publication Date: February 1, 1967
• Content Type: MFR

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NPIC/TDS/D-666-67
1 February 1967
SUBJECT: Photobleach Photography; Evaluation of Final Report Phase II
1. Photobleach studies, Phase II, was entered into with the
on 15 June 1965 for the purpose of extending the funda-
mental work on the reaction mechanism of the photobleach process initiated
in Phase I the previous year. Other goals of Phase II were:
a. To continue studies of the relationship between the
photographic properties and the operating variables to obtain
use information of the material.
b. Formulation of suitable dyes and test films.
c. Demonstrate the feasibility of achieving the objec-
tives established at the outset of Phase I.
2. The objectives established for this development under Phase I are
as follows:
a. A black and white (or colorless) film, with D max of 3.0
or more over the visible region, and a D min of 0.05 or less.
b. A resolution capability of 400 line pairs/mm.
c. Speed equivalent to ASA 0.1.
d. Ability to control the H&D curve from gamma 0.8 to
e. Stable storage of material, both before and after
exposure for at least one year.
3. Early in Phase II it became obvious that several of the objectives,
such as speed and'D max, would not be achieved. There did however, appear
to be a good possibility of achieving a photobleach material of lesser speed
and maximum density. Therefore the effort was re-oriented toward a set of
interim objectives of:
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SUBJECT: Photobleach Photography; Evaluation of Final Report Phase II
a. D max of at least 2.0 and a D min of 0.10.
b. Resolution of at least 200 line pairs/mm.
c. Latitude of 11 steps of a 0.15 gradiation density
step wedge.
d. Control of gamma from 1 to 2.
e. Storage for one year before exposure and six months
after exposure, and
f. Speed sufficient to expose a 4 x 5 inch sheet in no
more than 30 seconds.
4. Much of the first six months of Phase II was spent experimenting
with various dye combinations in an effort to obtain a material having good
D min and D max characteristics and capable of being heat locked to prevent
deterioration. Section III of the report (Alternate systems) deals with many
experiments that were made concerning such matters as; photosensitive agents,
dyes, additives, polymers, and heat locking. It was not until October 1966
that a formulation, "TMI", (Trimethylindoaniline) in combination with iodoform
suspended in an alcohol butrate polymer (ASB), was produced that exhibited
the desirable characteristics of density, speed, latitude and locking, or
keeping qualities. Therefore most of the report is devoted to extolling the
qualities and possibilities of this material.
5. Much progress has been made toward meeting the above interim objec-
tives, as shown in exhibits contained in the report, figures, la, lb, 2a,
2b, and 4:
a. Figure la is a film sample of the photobleach material
and, except for the blue color, is a fairly faithful reproduction
of the original, which is shown by comparing figures 2a and 2b
one of which (2b) is made from the silver halide original the
other (2a) is made from the photobleach film figure la.
b. Figure lb represents an initial attempt to coat paper
with photobleach. It is not very good, as of now, but does indicate
possibilities in this direction.
c. The resolution possibilities of the photobleach film are
shown in figure 4 which resolves about 200 lines/mm.
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SUBJECT: Photobleach Photography; Evaluation of Final Report Phase II
d. Since the writing of the report, reproductions of a
gray scale have been received (the reproduction and the step
wedge from which it was made are included with figure la).
When viewed with light passed by a series OA (yellow-green)
filter, it shows a latitude of about l4 shades of gray. Also,
from observation of this strip under filtered light, it is
reasonable to accept the D min and D max figures of 0.1 and
2.0 respectively as stated in the report as having been achived.
e. The heat development technique discussed in the
report has provided a reasonable storage capability and the
samples supplied with the report will not fade when exposed
to white light. However, the development time of two min-
utes far exceeds the desired time of 30 seconds for each
print. It is interesting to note, however, that the film
is relatively insenstive to all but ultra-violet light, which
is used for exposing.
f. The report shows little or no effort toward gamma
control; however, the report does state that with the appli-
cation of heat during the exposure there was an observed shifting
of the slope of the H&D curves. The means for controlling
this shift and the lower and upper limits of gamma are not
presently known.
6. The recommendations for further work on photobleach cover such
matters as:
a. Optimization of the latest film formulation.
b. Standardization of operational procedures.
c. Extend the investigation of contrajt or gamma control.
d. Develop appropriate packaging for the sensitized
material.
7. Inasmuch as the contract on this project has been terminated no
action on these recommendations will be taken at this time. However, because
of the great progress made on photobleach during the last few months of the
contract, further investigation should be made at some future date.
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SUBJECT: Photobleach Photography; Evaluation of Final Report Phase II
8. Because of the great difficulty anticipated in developing a black
photobleach film, further effort in this direction is not recommended at
this time.
Attachment:
Final Report on Photobleach Photography Phase II
Distribution:
Original & 1 - Route and File
1 - Originator
2 - TDS/DS
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 SECRETARY ,0 6~ i II
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BRANCH CHIEF
ORIGINATOR
TYPE SMOOTH
ORIGINATOR
CHIEF, DS
!D/CHIEF, DS
ASST) FOR TD
71 1 . , 74
DATE
L
ROJECT NO ? O O
D/CH, DS
ORIGINATOR
SEC. FOR
FILING
DATE OF FINAL DISPOSITION:
COMNMENTS : 2
E
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Photobleach Photography
25X1
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I. Introduction
II. Objectives and Status
III. Alternate Systems
IV. Recommendations for Further Work
V. Acknowledgments
Figures
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Page
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1 a. TMI Film
lb. TMI Paper
2a. Enlargement Made from TMI Film
2b. Enlargement Made from Original
3. Absorption Spectrum of TMI Film
4. Photomicrograph of Resolution Chart on TMI Film
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The progress made in the second year's effort in the development of
the Photobleach Photography process is described. A blue film has been
developed which bleaches to a clear neutral, and is developed and fixed by a
short heat treatment. This film, which satisfies most of the requirements
for a photocopy material, is described in detail. A sample of the film is
attached, as Figure 1.
The work leading to the development of the above film is described.
Several photosensitive agents have been evaluated, including chlorine-
containing polymers. Many dyes have been screened. Dyes which do not
complex with, and transfer energy to the photosensitive agent have
advantages in more rapid heat fixing. Several additives have been tested
for increase in photosensitivity of the photobleach system. One additive
appears promising. The chemical nature of the polymer film has been found
to markedly affect the sensitivity of the film.
The mechanism of the photobleach reaction is ascribed to the photolytic
formation of acid which reacts with the dye, thus bleaching it. A new process
is described in which photolytic formation of base similarly bleaches some
dyes.
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Photobleach Photography is in its present form a system for the
reproduction of monochrome direct positive copies of transparencies. The
system is dry, rapid, and has high resolution. In brief, the system consists
of a polymer film, containing a bleachable dye and a photosensitive agent,
cast on a suitable support, such as Mylar, glass or paper. Light passing
through the portions of the transparency with low optical density causes a
reaction to take place in the photobleach film which results in the bleaching
of the dye. In some cases the bleaching takes place immediately, in others
a post-exposure heat treatment speeds up the reaction. The heat treatment
also fixes the film so that it is no longer sensitive to light.
This process has been under investigation in these laboratories for the
past two years. The results of the first year's work have been described in a
final report, "Black and White Films", which describes in detail the apparatus
and techniques employed in the study. These descriptions will not be repeated
in this report.
This report will describe the results of the second year's effort (labeled
Phase II) of the Photobleach Photography project. During the year, work has
proceeded on a large variety of dyes and systems. Toward the end of the year,
a film was developed which shows most of the desired properties in a photocopy
system. Since this film is likely to be of the greatest interest, it is described
in detail in Section II. The properties which have been sought, and the degree
to which the film achieves them are detailed. In Section III, the work on other
film systems, which have proven to be less successful, is described. This
effort included screening of new materials, evaluation of modification of the
process and of new processes, and further exploration of the mechanism of the
reactions involved in the process. Recommendations for further work are
summarized in Section IV.
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II. OBJECTIVES AND STATUS
A. Objectives
The objectives of the Photobleach Photography program are
defined in terms of the properties of the photocopy material to be developed
in the course of the program. Two sets of objectives exist: first, the
properties to be desired ultimately in a material after a continued development
effort, and second, the properties desired in a material that can find
immediate application, developed as the result of the current year's work.
The second set of objectives, which are of immediate concern, are as follows:
1. Density: A black starting material with Dmax at least 2. 0,
which bleaches to a material with a fairly uniform absorption
in the visible region with a neutral color and a Dmin of 0. 10
or less.
2. Sensitivity: Sufficient to permit a demonstrated capability
of producing a 4 x 5 contact print with an exposure of not
more than 30 seconds, using a light source of less than
1100 watts power.
3. Resolution: 200 lines /mm.
4. Latitude: 11 steps of a 21 step tablet.
5. Storage capability: One year before exposure, six months
after exposure.
6. Gamma control: In the region from 1 to 2.
To put these objectives into historical perspective, the proposal
for the program under review was written in terms of more stringent require-
ments for density, sensitivity, and resolution, but did not predict that these
requirements would all be met in a single material. It stated further that work
on contrast control would be deferred to a Phase III program, as would the
attempt to derive a single photocopy material having all the required properties.
The objectives listed above were later agreed upon, in January 1966.
In this section, the properties of the available formulation which
best meets the requirements for a photocopy material will be dscribed. This
formulation was first tested in October 1966, and has not been optimized as to
relative proportions of the several component materials. Nevertheless, it
meets all the requirements listed above except for Dmax and for the range of
contrast control. This formulation (hereinafter the TMI film") consists of a
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single dye, TMI (N, N, 2-trimethylindoaniline), the photosensitive agent
iodoform, in Eastman alcohol soluble butyrate polymer (ASB) on a Mylar,
glass or paper substrate. On the premise that a sample is worth a page of
description, examples of contact copies on Mylar and on paper of a positive
transparency aerial photograph are shown as Figure 1. Figure 2 shows
enlargements of photographs taken of the original positive used to make
Figure 1, and of the copy made on TMI film, photographed through a yellow
filter.
Another dye, DEMI (N, N diethyl-2-methylindoaniline) gave
preliminary results similar to those of TMI, but has not been tested as
extensively. The following discussion applies specifically to the TMI film.
It is probable that DEMI films would give results differing only in minor
details from the TMI results.
1. Density. As can be seen from the example in Figure 1,
the material is a deep blue, bleaching to a clear transparent neutral tone.
Figure 3 shows the absorption spectrum of a typical film both before and after
.exposure and development. The optical density is 2 or greater for the film
depicted over the wavelength range of 5500-6300 A. Thicker films have been
made, having considerably greater optical density, and Figure 3 should not
be considered to represent the maximum or even the optimum optical density.
For the film depicted, the optical density of the bleached film less than 0. 1
at wavelengths above 5700 A, rises slowly to 0. 2 at 5000 A, and more rapidly
at lower wavelengths. The dashed line in Figure 3 is the absorption spectrum
of a Wratten #16 filter which is yellow. When viewed through this filter, the
TMI film appears black and yellow rather than blue and clear.
A thicker film, or one with a higher dye concentration,
will have a greater optical density, and the bleached film will also have an
increased optical density in proportion. Thus, if the optical density at 6000 A
is increased from 2. 5 to 4. 0, the density of the bleached film will be increased
from 0.10 to 0. 16, and the density range will increase from 2. 4 to 3. 8.
Comparing the absorption curve for the yellow filter with that of the photobleach
product at low wavelength, it is apparent that a rather large increase in the
amount of bleached product would be needed to materially affect the color
produced by it.
2. Sensitivity. The TMI film is sensitive primarily to light
at wavelengths of about 4000 A and below. It is not at all sensitive at
wavelengths above 5000 A. For these reasons, the most effective illumination
is a mercury lamp with a relatively high output in the 3660 A band. We have
used a 400 watt mercury lamp with a built-in reflector for
exposure. a is ance of 20 cm, exposures of 3 to 15 seconds have produced
acceptable results, when followed by oven development of eight minutes at
100?C. When the distance is increased to 40 cm, the times are increased to
10 to 40 seconds. The particular light source used in our laboratory is not
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sufficiently uniform to give consistent results over the area of a 4 x 5"
photocopy at the shorter lamp to copy distance. In this sense, the photographic
quality is better at the greater distance. There is no fundamental reason,
however, to prohibit the manufacture and use of a 400 watt lamp which will give
flat field illumination at relatively short distances, and thus permit short
exposure times. In any event, the sensitivity is well within the stated
specifications.
Heat development is needed to bring out the picture with
this system. Very little experimentation has been done with time or
temperature. In one trial, heating for two minutes at 120?C produced good
development. The time can probably be decreased further by raising the
temperature. We have no data as yet, however, on the effect of higher
temperatures on the dimensional stability of Mylar.
3. Resolution. A photomicrograph of a copy of a resolution
chart, which gives 226 line pairs/mm on TMI film is shown in Figure 4; 204
line pairs/mm were resolved in this photomicrograph.
4. Latitude. The TMI film has shown as many as 13 steps of
a 21 step tablet (0. 15 optical density steps), although 11 is more usual. The
latitude therefore appears to be adequate to the requirements.
5. Storage. There has not been enough time to evaluate the
storage, stability of the material. Unexposed material loses its sensitivity
over a period of a day or two if left open to the atmosphere. When properly
packaged, however, sensitivity has been maintained for a month, which was
the period available for the test. There seems to be no reason to believe that
sensitivity of properly packaged materials will not be maintained indefinitely,
Exposed and developed films have been exposed in a 400 watt
projector for over 20 minutes with no noticeable fading. Such films left in the
open in the laboratory for a month have shown no signs of deterioration. It is
expected that the films will be stable indefinitely under normal storage
conditions, such as are used for color transparencies.
6. Gamma control. No specific work on gamma control of the
TMI film has been done. It is expected that gamma can be controlled by control
of the development heating period, the exposure, or both, but since no data is
available, no definitive statements can be made.
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This section of the report will summarize the work on systems other
than the TMI film described in Section II. Several of these have interesting
properties, although none have been as successful as TMI in fulfilling the
requirements for a photocopy material. Work has been done in several areas,
including screening of dyes, polymers, and photosensitive agents, extensive
studies on particular dye systems, effects of external parameters on
photographic properties, and mechanism studies. These will be briefly
summarized.
Screening Experiments
1. Photosensitive agents. The first photosensitive agent used
in the Photobleach Process was iodoform. During the course of the project
many other photosensitive agents were evaluated in order to find one with
superior properties. The main objection to iodoform is that it causes a yellow-
brown color to develop in the bleached areas of most systems, due to extensive
exposure. In those systems which are sufficiently fast, photographically, the
dark color does not develop. It follows, therefore, that the color is probably
due to a photodecomposition product of iodoform which is not necessarily
related to the dye bleaching reactions. Bromine and chlorine compounds were
expected to form products with considerably less absorption in the visible.
This has been found to be correct. The bromine and chlorine compounds
generally require exposure further into the ultraviolet than does iodoform,
however, and are also generally considerably more toxic. Iodoform itself is
relatively non-toxic -- it is used medicinally both internally and externally.
The photosensitive halogen compounds which have been
tested during the year include:
hexachlorocyclopentadiene
hexachlorethane
carbon tetrabromide
pentabromoethane
tetraiodoethylene
polyvinylchloride
polyvinylidenechloride
2, 3-bis(bromomethyl)-1, 4-dibromobutene-2
Hexachlorocyclopentadiene is an interesting photosensitive
agent in that it has no absorption in the visible, does not form products
absorbing in the visible, and is reasonably efficient. It has the disadvantage,
at least with some dyes, of spontaneously reversing the bleaching process on
standing at room temperature, in a period ranging from hours to days. Heat
locking is not needed for this agent when used with the class of dyes that do
not transfer energy.
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Polyvinylchloride and polyvinylidenechloride are polymers
used in making films, the latter being sold commercially as Saran. When
illuminated with ultraviolet, the films act as photosensitive agents, bleaching
dissolved dyes. The polyvinylidenechloride is the more sensitive of the two
polymers. With these materials heat fixing is not possible, and the dyes used
must be those that do not transfer energy. In addition, cases of spontaneous
reversal have been noted, although no effort has been made to determine
whether such reversal is a general phenomenon with these films.
The other photosensitive agents tested did not exhibit any
pronounced superiority over iodoform, and with the exception of carbon
tetrabromide, were not extensively evaluated. Carbon tetrabromide had been
used in the first year's program, and also saw considerable use during
Phase II, as in many cases it did not form the tan reaction products as
extensively as iodoform.
2. Dyes. Screening of dyes proceeded throughout the project.
In January, the dye Rose Bengal together with iodoform in the polymer RJ-100
was shown to be more sensitive than any preceding system. Dyes closely
related to Rose Bengal, that is, iodinated or brominated derivatives of
fluorescein, were shown to be similarly sensitive in the same environment.
These dyes were red, all having absorption peaks in the 5200-5600 A region.
Bleaching was rapid and clean, with the formation of a clear product of
neutral density.
In order to produce a black mixture, dyes are needed whose
absorption covers the visible spectrum. Rose Bengal and related dyes cover
the central portion of the visible region, and promising yellow dyes were known
for the short wavelength region. The known blue dyes, however, were all too
slow, and several of the best dyes bleached to colors other than neutral gray.
The main screening effort was made for the blue dyes. A search was instituted
for green dyes also, but very few green dyes with reasonable bleaching
properties were found.
The blue dye with the greatest apparent promise for a black
mixture was pinacyanole. This dye is in the cyanine class. It gives a good
blue color in films, bleaches to a clear film, and is relatively fast. A black
film with good photographic properties was developed from pinacyanole,
together with Rose Bengal and p-amino-benzilidenerhodanine. This film,
however, proved impossible to heat lock. Despite early experiments indicating
light stability, pinacyanole was later found to be insufficiently stable to be used
in a film.
Several other blue cyanine dyes were extensively investigated,
but none were found to have all the essential properties simultaneously. Some
were found to be essentially insoluble in all the polymers being used. Others
formed a complex with the photosensitive agents with a much paler color than the
original dye. Some were not stable to light.
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A green dye, Bindschedler's Green, was found to have
excellent photosensitivity in solution. It was not found possible, however,
to cast a film in which the dye maintained its color, or showed photobleaching
properties. The structure of the dye is related to that of Indophenol Blue,
one of the earliest dyes utilized in the photobleach system. Since the solution
photosensitivity of the Bindschedler's Green was so great, and since the
Indophenol Blue gave good, although slow, blue films, a thorough search was
instituted for other dyes of related structure. None were found to be
commercially available. A literature search revealed that a few similar dyes
had been synthesized in the past. Two of these were selected, and were
custom synthesized by Eastman Kodak for us. These are the dyes, TMI and
DEMI, described in Section II.
The dyes, TMI and DEMI, although they exhibit the interesting
properties described in Section II, are not suitable for mixtures with Rose
Bengal. The dyes develop on heating, and are thus faster than Rose Bengal.
In addition, there is evidence that Rose Bengal transfers energy to the other
dyes. This was demonstrated with mixtures of Rose Bengal and Indophenol
Blue in which the Rose Bengal bleaches more slowly than if alone, and the
Indophenol Blue more rapidly. A multilayer film might avoid the latter problem,
but would introduce other undesirable attributes, such as thicker films and
hence lower resolution, and greater difficulty in heat locking.
3. Additives. Several additives were tested during the program
to determine if they had any positive effect on photosensitivity. These included:
N-vinyl pyrrolidone
allyl alcohol
9-vinyl carbazole
1 -allyl- 2 -thiourea
anethole
Of these, N-vinyl pyrrolidone showed a variable effect on the bleaching rate of
some dyes in polyvinylpyrrolidone films, as high as a factor of 1. 5 to 2, and
no effect with other dyes. The other additives showed no effect, except for the
allyl thiourea, which killed the bleaching reaction.
4. Polymers. Several experiments comparing rates of
bleaching of similar systems in a variety of polymers showed no effect of
polymer on bleaching rate. In December, a new polymer, RJ-100, a
copolymer of vinyl alcohol and styrene, was investigated, and showed an
increase in bleaching rate of a factor of four or more with some dyes and no
effect with others. Dyes which were particularly improved included Rose
Bengal and Indophenol Blue. Quantitative assessment of the effect on bleaching
rates became difficult, as an induction period exists with these combinations.
That is, there is little apparent change in optical density after a short exposure,
but several minutes later, bleaching of the exposed areas takes place while the
film is in the dark.
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Another polymer, Arochlor (Monsanto), when used as an
additive to RJ-100, increased the speed even further. However, the Arochlor
acts as a sensitizer, and the films cannot be completely desensitized.
Therefore, RJ-100 alone was used as the polymer of choice throughout most
of the project year.
When coated on a flexible substrate, RJ-100 tends to crack
after a period of time, In October, a flexible polymer, Eastman alcohol
soluble butyrate, ASB, was found which seemed to give as good results as
RJ-100, without the disadvantage of cracking. A thorough quantitative
comparison of bleaching rates in the two polymers has not been made, however.
ASB is the current polymer of choice.
A polysulfone polymer has been tested which has the property
that a coherent film of polymer can be peeled off a glass substrate. A film
made up on glass and exposed and locked in the usual way can then be stripped
from the glass and mounted or otherwise handled by the user. The dimensional
stability of the detached films was not sufficiently high to warrant further
effort.
B. Parametric and Exploratory Experiments
In this section, experiments designed to evaluate the conditions
of use of the photographic system and to explore alternate systems are
described.
1. Heat locking. The process of locking or fixing the film by
means of heat has been under continuous scrutiny. Observations have been
qualitative, for the most part, consisting of determining which of various time
and temperature combinations lead to satisfactory heat locking. Heat locking
conditions have been found to vary widely, and depend on the dye, the
photosensitive agent, the polymer and its thickness, and the substrate. To
illustrate, a Rose Bengal film will generally need a longer heat locking period
than a similar film using Indophenol Blue. A film based on iodoform will
generally lock more rapidly than one based on carbon tetrabromide. A
polystyrene film will lock more rapidly than one based on carbon tetrabromide.
A polystyrene film will lock more rapidly than a similar composition in
RJ-100. A film on Mylar will lock in one tenth to one fifth the time of the same
composition on a glass substrate. A thick film will take longer to heat lock
than a thin film. In addition, thermal reactions take place in some cases. For
example, Rose Bengal-carbon tetrabromide films cannot be heated above about
110?C or they will thermally bleach. As can be inferred from the above, it is
necessary to determine the optimum heat locking conditions for each
formulation independently. Most of the work has been done with films on glass.
For films on glass, heating time roughly doubles for every ten degrees drop in
temperature. At 110?C heating time for films on glass ranges between
30 minutes and two hours. The TMI film on Mylar tapes is locked completely
in six to eight minutes at 110?C.
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Several experiments were performed using vacuum to aid
locking. These experiments were based on the hypothesis that locking is due
to evaporation of photosensitive agent and that evaporation would be more
rapid in a vacuum. Results were not consistent, and the improvement shown
thus far does not indicate that vacuum will shorten the locking time appreciably.
2. Packaging. It has been observed that photobleach films are
more sensitive when freshly prepared than after storage. The effect ranges
from a loss of about 500%o on storage for some months for some films to
complete loss of sensitivity in two days for the TMI film described earlier.
The effect is ascribed to evaporation of the photosensitive agent. It has been
shown that packaging the TMI film in aluminum foil will prevent the loss of
activity. It has also been shown that a TMI film with iodoform omitted will
become sensitive if it is stored in a closed container containing iodoform. The
iodoform vapor diffuses into the film and imparts photosensitivity.
Although experimentation on packaging has not been
extensive, we feel that we have demonstrated that a reasonable shelf life with
high sensitivity can be maintained for the photobleach materials through
appropriate packaging.
3. Contrast control. Brief experiments to determine the effect
of heating during exposure have been performed. H & D curves (optical density
plotted against log exposure) were plotted for several runs on two samples of
a Rose Bengal iodoform film. For one sample, the film was held at room
temperature during one run, and heated by a stream of warm air during the
other. The slopes of the respective H & D curves were 1. 6 and 2. 0. The
second film was run with two, one and no heat filters interposed between film
and light source during exposure. The slopes for these runs were 1. 8, 1. 9,
2. 0. These experiments demonstrate that the slope of the H & D curve can be
increased by heating during exposure. No experiments were run with
photographic subjects, however, so the question of whether this procedure will
affect photographic contrast is still not resolved.
If contrast control is desired for the TMI films, an
additional processing variable is available. The temperature and time of
post-exposure heating probably have an effect on the contrast and latitude
achieved by the films. These effects have not been investigated as yet, and
should have a high priority in any future work on these materials.
Experimental studies on the mechanism of the photobleach reactions
received much less emphasis than in the preceding year. Three of the experi-
ments related to mechanism will be briefly discussed.
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1. Acid formation. The experiments on the mechanism of
anthraquinone dye bleaching consisted of illuminating samples of dyes in films
with CHI3 as photosensitive agent for successive short periods of time and
obtaining absorption spectra after each exposure. The same dyes in ethanol
solution were treated with successive small portions of concentrated
hydrochloric acid, and again absorption spectra were obtained. The initial,
final and intermediate spectra were similar in both cases, indicating that
reaction with acid is responsible for the bleaching process. Further, a
completely bleached film was dissolved off the slide, and sodium hydroxide
added. The solution then changed color, to the original color of the dye.
This latter experiment was also successful using Indophenol Blue, which is
not an anthraquinone. It now seems reasonably certain that the mechanism
for anthraquinone dye bleaching involves neutralization by strong acid formed
from the photo decomposition of the photosensitive agent. Although the
evidence is less clear for other dyes, it is probable that the same mechanism
applies for all the reactions studied.
2. Azide process. As indicated above, the mechanism of the
photobleach reaction is believed to be the reaction of an acid with a dye. Some
dyes also change color, or bleach, in the presence of base. A photochemical
reaction, the photolysis of sodium azide, was found in the literature which
results in the formation of base, in this case NH3 and OH-. A film was made
up using a dye which bleaches in base, in addition to the photosensitive agent,
sodium azide. The film bleached when exposed to the strong 2537A Hg line,
but not when exposed only to longer wavelength radiation. This observation
supports the mechanism assignment, and also leads to a new photobleach
process. The one dye examined did not transfer energy to the azide, in the
way that some dyes transfer energy to iodoform in the "acid" photobleaching
process. The process was not investigated further because of the very low
wavelength required, which is not transmitted through glass or through most
photographic materials.
3. Complex formation. Experiments on two methine dyes gave
strong evidence for the existence of a complex between dye and iodoform. In
these cases, film made up with dye and iodoform were considerably lighter in
color than expected from the dye alone. They darken on heating to drive off
iodoform, and then bleached when heated in iodoform vapor. None of the other
dyes examined for this behavior responded in the same way. The results,
however, are significant in that they demonstrate the formation of a complex.
These effects were very pronounced for the two methine
dyes. In the more common situation, the formation of a complex leads to a
slight shift of wavelength, and to small change in extinction coefficient. The
careful, quantitative work needed to verify the formation of complexes of
other dyes was not undertaken.
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 Approved For Release 2005/06/23 : CIA-RDP78BO477OA002800030036-1
Another interesting experimental result can be explained
on the basis of complex formation. Rose Bengal requires considerably more
heating for locking in a given film than does TMI, and Rose Bengal transfers
energy to iodoform, while TMI does not. The formation of a complex between
Rose Bengal and iodoform, and the lack of a complex between TMI and
iodoform would explain both of these observations. A complex between Rose
Bengal and iodoform would tend to slow down the evaporation of iodoform, and
would allow the transfer of energy from the dye molecule to its partner.
Generalizing, it is probable that all dyes that transfer energy do so because
they have formed a complex with the photosensitive agent, while those dyes
that do not transfer energy are not involved in a complex.
-11-
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 Approved For Release 2005/06/23 : CIA-RDP78B04770A002800030036-1
Several alternative approaches to the exploitation of Photobleach
Photography are available. The approaches to be discussed here are:
(1) optimization of TMI film, (2) extension of TMI film to black, and
(3) extension of earlier work.
1. Optimization of TMI film. The TMI film is essentially ready
for use. It meets the requirements for a photocopy film, except for the blue
color in place of black and the present lack of contrast control. If the film
will serve the purposes for which it was designed, as we believe it will, then
it should be put to use. For this to be done, further work is needed in the
following areas:
a. Optimization of film formulation. Further experimentation
with the relative proportions of the ingredients of the film should be done, as
well as on coating procedures, and film thickness.
b. Standardization of exposure and development conditions.
c. Gamma control. The possibility of the control of contrast
should be thoroughly explored.
d. Standardization of packaging.
e. Design and construction of equipment to be used by the
customer in the utilization of the TMI film.
It is expected that the work in the first four of these areas would
be completed in about six months, at a cost of about one fourth of that for the
Phase II program. The design and construction of equipment could be done
simultaneously, at additional cost.
2. Extension of TMI film to black. The investigation of the TMI
film to determine a dye or combination of dyes which will produce a black
film would be considerably more difficult than the optimization of the blue
film. A large number of dyes must be screened to determine compatibility
with the TMI film. Dyes must be found with the proper color, solubility,
and sensitivity characteristics. Further, they should be dyes which do not
transfer energy, while most of our experience has been with dyes which do
transfer energy.
For a reasonable probability of success with this problem, a
one year program at about the past year's level of effort would be required.
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 Approved For Release 2005/06/23 : CIA-RDP78BO477OA002800030036-1
3. Extension of earlier work. The success achieved with the TMI
film and the properties demonstrated by it have caused us to re-evaluate the
desirability of continuing work along previous lines. It now seems clear
that non-complexing dyes have a clear superiority from the heat-locking point
of view. We therefore recommend that no further work be done with complexing
dyes (such as Rose Bengal) in the immediate future.
4. Recommendation. We feel that the program for optimization of
the TMI film, described in paragraph 1 above, would give the greatest value
per program dollar. If the TMI film is put into use, and found useful, but
the blue color remains a handicap, then the second program, for extending
the TMI film to a black, should be implemented.
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 Approved For Release 2005/06/23 : CIA-RDP78BO477OA002800030036-1
Many helpful and stimulating discussions held with
25X1
contributed much to the progress of the project. The
laboratory work was done b I whose skill and 25X1
ingenuity also contributed g
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 ___Approved For Release 2005L06/23 C1A-RDP_78B04770A002800030036-1
III li ,:~:
mmw_
Figure la. Sample of TMI Film
Figure lb. Sample of TMI Paper
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 Approved For Release 2005/06/23 : CIA-RDP78B04770A002800030036-1
Figure 2a. Enlargement Made from TMI Film
Figure 2b. Enlargement Made from Silver Halide Original
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 4 I ) ci
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Wratten #16 filter
1.0
TMI film
before
bleaching
TMI film after bleaching
5000
Wavelength, Angstroms
6000 7000
Figure 3. Absorption Spectrum of TMI Film
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 Approved For Release 2005/06/23 CIA-RDP78BO477OA002800030036-1
r R
`?a
Figure 4. Photomicrograph of Resolution Chart on TMI Film
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 Approved Far Release 20P5/06/23 : CIA-RDP78BO477OA002800030036-1
Photobleach Photography
25X1
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 25X1 Approved For Release 2005/06/23 : CIA-RDP78BO477OA002800030036-1
Next 22 Page(s) In Document Exempt
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 Approved For ease 2005/06/23 :.,rCIA-RDP78B04772800030036-1
6 January 1967
Dear Will:
Attached are films which Max prepared in response
to your telephone request. I hope these will be
suitable for your requirement. If not, let us know.
25X1
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 Approved For fpse 2005/06/23: CIA-RDP78B047702800030036-1
5X1
Contract No.
Task No. 02
Progress Report No. 14 (FINAL)
Covering the period October 15 - November 30, 1006
Financial Status
Amount Authorized . . . . . . . . . . . . . . .
Estimated Expenditures thru 11/30/66 .. . . . .
Funds Committed
Funds Remaining
*Subject to adjustment as final bills and credits
are received.
Technical Status
The final technical report was submitted on 7 December
1966.
?5X1
6 January 1967
Distribution:
Technical Representative - three copies
File - one copy
25X1
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 Approved For. Release 2005/06/2WWIARpP78B0477OA002800030036-1
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