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A Few Words About
Archival Print Processing
Traditional photography relies on the light sensitivity of
compounds
based on silver plus chlorine and/or bromine, which make a
salt.
Tiny grains of this salt are distributed in gelatin to make
an
emulsion. When light strikes the emulsion, the silver
compound
changes
chemically. The more light, the bigger the
change. A
chemical
bath (the developer) reacts with the exposed salt grains,
turning them
to metallic silver grains, which are black to the eye.
These
grains form the image. The more light and/or
development, the
darker the emulsion.
Basically the same process occurs in film and printing
paper, only the
substrate is different. Printing paper has a
white coating
under the emulsion, to boost the brightness of
highlights. Film
is necessarily clear to allow light to shine through when
making
prints. Both substrates to carry a thin coating of the
silver-gelatin emulsion. Yes, it's the same gelatin
found in
desserts, extracted from bones, but treated to make it much
tougher,
physically. For example, an acid bath hardens the
gelatin to
resist scratching.
After development, the emulsion still contains all the
original
grains; some have been converted to black silver, some
are still
in the form of the salt. "Fixing" the image dissolves
the salt
grains, removing them from the emulsion, so only the
developed
grains remain to form the image.
Potential problems:
- Failure to remove all the undeveloped grains.
Over
a long time they may revert to metallic silver, creating
unwanted
black areas in the image.
- Failure to remove the fixer, the chemical that
dissolved undeveloped grains. An acid, fixer may
corrode the
black silver grains to make them invisible, weakening
the image.
- Chemicals in the atmosphere corrode silver grains,
destroying the image.
Archival processing addresses all three threats.
- Thorough fixing ensures full removal of undeveloped
grains.
- Additional chemical treatment and washing remove
almost all
fixer (a slight trace actually stabilizes the image).
- Toning the image to "armor" the silver grains for
protection from later attack by chemicals.
Toning coats each silver grain with a chemically bonded
layer that
resists later chemical activity better than pure
silver. Toning
may or may not be visible.
Selenium is our standard toning material, applied as a
"final bath" in
the darkroom process. When used to enhance longevity,
selenium
darkens the image slightly, increasing contrast. When
left in the
selenium solution for longer times, prints take on a "warm"
tone,
shifting from a neutral black. Extended toning changes
the color
of the developed grains from black to reddish brown, giving
prints an
"antique" appearance that in the past resulted from aging or
toning.
To finish its protection, a print is mounted on a stiff
board that
resists folding and tearing. The mount also prepares a
print for
framing.
When framed under glazing , a print must not be placed
directly
against the glass or acrylic. To separate the print
from the
grazing, a mat board is placed on top of the mount, with a
window cut
our to reveal the print.
For full archival treatment, mounts, mats, the adhesive that
holds the
print to the mount, and the frames must all be free of
acid. Wood
frames are lined with a separator to prevent anthing in the
wood from
migrating through the mount to the print.
If our prints don't last 100 years, we'll make another one
for
you. ;-)
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Why Film?
A medium-format black and
white negative (2.25 inches square or slightly larger)
contains more information than as a 90 megapixel
digital image. The most expensive digital
cameras are only recently approached this level of
resolution. Large format
negatives exceed 200 MP.
Film resolution allows prints
larger than 16x20 inches to appear sharp even when
examined from close
up.
Modern
film, on a base of polyester, lasts as long as
prints--more than 100 years. That's
good
for making prints later--no worry about a digital
storage medium
growing obsolete and unreadable.
To top it off, a film image is an
historical object--it was present at the event in the
picture.
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