 |
CHEMISTRY
of PHOTOGRAPHY |
@CSU Stanislaus |
CHEM 2502 Chemistry of Photography
Laboratory
Section 4 -- Some
Alternative Processing Experiments
In this section several
alternative types of processing will be studied. These include
reversal printing (Experiment 1), toning (Experiment 2), and solarization (Experiment 3).
If necessary prepare a
developer as done for Section 1,Experiment 5. The purpose
is to study the conditions necessary to make a reversed image.
- Step 1 Set the
Variac to 65. Then expose the contact print (composed of
the usual negative and photographic paper) for 30
seconds. Develop the print until you see a
"good" picture (about 20-30 seconds).
Immediately wash the exposed photographic paper under tap
water for about 10 seconds.
- Step 2 Place
the washed exposed photographic paper directly into the
bleaching solution which has been provided. As soon as
the picture disappears, wash the bleached print under tap
water for about 10 seconds.
- Step 3 Place
the print in the clearing solution (also provided) for
10-15 seconds and blot the print dry with a paper towel.
- Step 4 Place
the print under bright light for 30 seconds. Using the
normal solutions, develop (20-30 seconds to obtain a
"good" picture). Stop, fix and wash as you have
done previously. Record the results.
The purpose of
this experiment is to determine the effect of exposure times on a
solarized image.
- Step 1 Prepare
fresh developer, stop bath, fixer and wash (if
necessary), according to Section 1, Experiment 5.
- Step 2 With
the Variac set at 35, expose photographic paper through a
negative for 30 seconds. Place in the developer, stirring
continually, until a print with good contrast is
obtained. Record the developing time. Stop, fix and wash
as before. We will refer to this as Print 1.
- Step 3 Prepare
Print 2 in the following way. Expose the print for 15
seconds, and place in the developer. When the image can
be seen but is still very light, remove the print from
the developer, noting and recording this initial development
time. Place under the light on a paper towel and expose a
second time (without a negative) for 15 more seconds.
Finish developing the print until a good image is formed.
Record this developing time also. Stop, fix and wash as
before.
- Step 4 Prepare
two additional prints by the same method as Step 3 but
for the first print decrease the initial exposure to 5
seconds and increase the second exposure to 25 seconds.
For the second print use an initial exposure of 25
seconds and a second exposure of 5 seconds.
- Step 5 Compare
prints 1, 2, 3, and 4. How does the second exposure
affect the image? Do the different exposer times cause a
change in the image? Why doesn't the print turn
completely black during the second development?
The process of toning
involves a change in the color of a print. This can be achieved
by replacing the precipitated silver metal by other metals or by
colored insoluble compounds. The purpose is to
illustrate several toning reactions and to determine, for each,
how the final image is affected by the time spent in the toning
solution.
- Step 1 Prepare
10 prints according to Section 1, Experiment 5.
- Step 2 Iron
Toning Prepare an iron toning bath by mixing 10.0 mL
ferric ammonium citrate (10% solution), 10.0 mL of K3Fe(CN)6
(10% solution) and 100 mL of a 10% solution of acetic
acid. Place prints in this solution for 1, 5 and 9
minutes. Remove the prints from the solution and rinse
them. Record the results. [These chemicals may be disposed
of in the drain]. What chemical reactions account for the
color changes you observe? Where does the silver go? Why?
- Step 3 Copper
Toning Prepare a copper toning bath as follows.
Dissolve 1.07 g of K3Fe(CN)6 and
5.33 g of potassium citrate in 200 mL of H2O.
In a separate beaker dissolve 1.33 g of CuSO4
and 5.33 g of potassium citrate in 200 mL of water. Mix
equal volumes of these two solutions just prior to using
them. Place prints in the solution for 1, 5 and 9
minutes. Wash them in deionized water. What color changes
do you see? [Because these solutions contain copper they
should be disposed of in the aqueous waste container .Write the
chemical equations which account for the color changes.
Which species are colored? Why are these not washed out
of the emulsion?
- Step 4 Sepia
(Ag2S) Toning - Place
prints in a 20% solution of Na2S2O3
for 5 minutes. The next step should be done in a
hood. Without
rinsing the prints, immerse them in a 3 M HCl solution
for 15, 30, and 60 minutes. What do you observe? What are
the chemical reactions? Why is it necessary to place the
print in the Na2S2O3 solution
before the HCl solution? [These chemicals can be disposed
of in the sink].
What conclusion can you draw about how the time in the
toning bath affects the resulting image?
j byrd
jim@chem.csustan.edu
m perona
mike@chem.csustan.edu