371
in which the daguerreotype plate and a block of silver
were attached to two separate wires and suspended in
a container of potassium cyanide. When the wires were
then connected to a wet battery, molecules of silver
were transferred to the plate through electrolysis. This
procedure became known as the “American process”
and was adopted by French plate manufacturers in
the 1850s as the new standard for the preparation of
daguerreotype plates.
Newly developed tools and methods for polishing
the silver-coated plates were introduced into the revised
process as well. Abrasive powders such as iron oxide
and decomposed limestone, fi ne pumice stones, buck-
skin- and silk-covered buffi ng blocks and wheels, and
jeweler’s rouge were used to bring plates to a mirror-
like shine. Careful polishing with such materials was
essential to ensuring that the silver coating was entirely
smooth and that the appearance of lines any other visible
imperfections was minimized.
Further experiments with the chemical sensitiza-
tion of the polished plate resulted in the introduction
of additional steps into Daguerre’s original process. In
late 1839 in Philadelphia, Robert Cornelius, the son of
a plated goods manufacturer, and Dr. Paul Beck God-
dard, a chemist, fi rst used bromine as an accelerator in
the sensitization process. Other innovators, like John
Frederick Goddard (an Englishman of no relation to
the American Goddard) and Franz Kratochwila (a Pol-
ish civil servant), experimented with bromine as well.
Antoine Claudet (a Frenchman working in London)
developed a technique for using bromine and chlorine
as accelerated sensitizing agents. This multi-phase
sensitization of the daguerreotype plate, in combination
with the larger aperture lenses used in cameras, reduced
exposure times from minutes to as little as three sec-
onds, depending on light conditions. These signifi cantly
reduced exposure times made daguerreotypy a practical
medium for portraiture.
Word of these innovations spread quickly, and da-
guerreotypists began exposing their iodine-sensitized
plates to bromine in the second of what was now three
steps in the sensitization process. Suspended face-down
in a box containing a mixture of bromine and quicklime,
the iodine-treated, gold-colored surface of the plate
turned a silvery blue. Subsequently, the plate was briefl y
re-exposed to iodine and its sensitization completed.
During each step, the progress of the plate’s sensitization
could be examined by viewing its tones through glass
windows in the different coating boxes.
Additional experiments in the chemistry of da-
guerreotypy also improved the durability of the image
on the daguerreian plate’s surface. In 1840, the French
physicist Louis Armand Hippolyte Fizeau discovered
that washing the fi xed plate with a weak solution of gold
chloride that had been heated and spread over the image
would enhance its tones as well as stabilize and preserve
it against further chemical reactions. Daguerreotypists
employed this gilding technique from its introduction
to the end of the daguerreian era.
Even when gilded, daguerreotypes remained fragile
and needed to be enclosed in a protective case behind
glass. Mass-produced cases made of leather and, later,
of an early type of plastic made from gum shellac were
sold to daguerreotypists. Brass mats of different shapes
and case linings of silk or velvet were added to the case
to enhance the appearance of the fi nished daguerreotype.
Customers could choose among the options in each to
embellish their portraits, while daguerreotypists used
stamped cases and mats to advertise their work.
A general desire for images that were both realistic
and aesthetically appealing drove much of the continu-
ing experimentation with the daguerreian process. In
1851, a daguerreotypist named Levi L. Hill in upstate
New York announced that he had discovered a process
for capturing vivid reds, greens, blues, and browns on
the silver daguerreian plate, resulting in images that
appeared even more lifelike and beautiful than the da-
guerreotype. There was good deal of popular excitement
about the advance, and Hill advertised manuals describ-
ing his process for three dollars. Yet when Hill delayed
displaying examples of his achievement in an effort to
perfect and patent his process, suspicions of a hoax were
raised. Upon applying for a patent, Hill testifi ed about
his process and fi nally displayed examples of his “hillo-
types,” as he termed them, to a Senate committee that
concluded that he could not patent a “strictly chemical”
process (qtd. in Barger and White, 41). Late-twentieth
century examinations of Hill’s process, as he detailed
it in his 1856 Treatise on Heliochromy and as it can be
studied through sixty-two hillotypes held by the Muse-
um of American History of the Smithsonian Institution,
have concluded that it differs signifi cantly enough from
daguerreotypy, despite Hill’s use of daguerreian plates,
to be considered a separate photographic process.The Popularity and Demise of the
Daguerreotype
By the mid-1840s, daguerreotype studios had been
established in most of the world’s major cities. The
profi tability of making portraits for an eager public led
many people from all walks of life to take up the practice
of daguerreotypy. Itinerant daguerreotypists went so far
as to improvise horse-drawn and shipboard studios and
in doing so, extended the practice of daguerreotypy to
the far reaches of the world. In 1840 in Rio de Janeiro,
the fourteen- year-old Brazilian emperor Don Pedro II
was so taken with a visiting priest’s demonstration of
the daguerreian process that he purchased a camera and
became Brazil’s fi rst photographer. In Australia, the fi rst