accelerates desorption of thiosulfate by an ion
exchange mechanism.
In the past, a ‘‘hypo eliminator’’ formula con-
taining peroxide was recommended. This treatment
chemically destroys thiosulfate to a harmless form,
but this solution is no longer recommended
because the treatment is now known to be harmful
to the image. Since the necessary washing time to
produce prints with good permanence is variable, it
is recommended to run a quality control test in
each darkroom. One test for residual thiosulfate is
called ‘‘silver nitrate test’’ and is facile and sensitive
enough for most purposes. The test should be run
at regular intervals, emphasising whenever the new
printing paper, fixing solution, or washing water is
introduced to the darkroom.
In past decades, conservation scientists or con-
servators found problems with the permanence of
silver-gelatin prints and microfilms that had been
properly processed and washed. The problems were
attributable to improper storage and display con-
ditions. Silver-gelatin materials enjoy very long life
expectancy if they are properly processed, washed,
and stored. Good storage conditions require low
temperature, low humidity, and absence of envir-
onmental pollutants and other oxidizing agents,
including those from the storage container ma-
terials, such as cardboard, wood, adhesives, and
paints. The image is also susceptible to pollutants
from industrial exhaust and oxidizing agents from
the atmosphere, such as ozone. While it is difficult
enough to keep valued photographs under ideal
storage conditions, it is virtually impossible if the
desire is to have easy access to them or indeed if
they are displayed.
In order to make the image more permanent in less
than ideal conditions, toning treatments of prints
have been found to be effective. In particular, treat-
ment with polysulfide toners (such as Kodak Brown
Toner) is convenient as well as inexpensive and has
been found to be highly protective in a number of
studies. Prints should be toned after fixing and wash-
ing. Prints must be thoroughly washed again after
toning to remove the toning solution, because resi-
dual toner is also detrimental to the image. Although
polysulfide toned images have increased stability,
proper storage conditions remain the key factor in a
photographic print’s longevity.
Environmental Concerns
Concerns for preserving the environment have also
been raised in recent decades. Volume processors
use efficient processing methods where waste solu-
tion is minimized, which is important in terms of
minimizing chemical waste and the cost of disposal
treatment. On the other hand, attempts were made
to reduce environmental impacts from the effluents
of small-scale darkrooms, which are discharged
directly into municipal sewer systems, by replacing
the rather harmful hydroxybenzene compounds
(developing agents such as hydroquinone, catechol,
and pyrogallol) with harmless ascorbic acid and its
isomers. The developing action of ascorbic acid
was known in the early 1930s and it was one of
the preferred developing agents among modern
researchers studying the mechanisms of develop-
ment. It was known, however, to be difficult to
make practical, robust developer solutions using
ascorbic acid. Environmental awareness re-directed
attention to these harmless compounds (ascorbic
acid is in fact vitamin C), and attempts to use
ascorbates are seen in patent literature for a range
of applications from low contrast, fine grain film
developers to high contrast medical imaging.
Major manufacturers sold developers that emp-
loyed ascorbates in place of hydroquinone in PQ
developer systems. However at the beginning of the
twenty-first century, this effort has lost importance
as most standard solutions already have low envir-
onmental loads and most amateur, commercial,
medical, and scientific photographers and photo-
journalists have rapidly migrated to digital imaging
technology, leaving only a small population of fine
art photographers in the world of traditional, wet-
processed materials.
There are many ways to look at the developing
processes and their history. It is important to note
that many darkroom manuals and photography
textbooks contain technical errors and repeat out-
dated misconceptions; interested readers are en-
couraged to consult original research publications
and review articles written by experts in a particu-
lar branch of developing processes. Coote (1982) is
a darkroom manual rather rich in technical aspects.
Mitchell (1984) is an introductory textbook of
photography as a general science class at college
level. At a more technical level, Keller (1993) and
Locker (1996) are encyclopedia sections giving con-
cise accounts of the photographic process. Haist
(1979) is a comprehensive book on the chemistry
of photographic processing. Sturge (1977) and
Proudfoot (1997) are handbooks for those inter-
ested in technical aspects of photography. The
newer edition of Sturge (1977) has a considerably
different content from the seventh edition. James
(1977) is a highly specialized technical reference
book for photographic chemists. Levenson’s
papers give overviews of development reactions
with emphasis on superadditivity, for which heDEVELOPING PROCESSES