Hannavy_RT72353_C000v1.indd

1161

Organic Processes

This category is rather diverse in the materials it embrac-
es, but all are purely organic, some macromolecular or
colloidal, and do not involve inorganic salts. The photo-
chemistry is not well-understood in all cases, but entails
colloid-hardening and dye-bleaching processes.
The oldest organic process was also the fi rst to pro-
vide a camera image that has survived to the present
day: the Heliographic process invented by Joseph Nicé-
phore Niépce around 1822, also known as the Asphalt
or Bitumen process. Bitumen of Judaea dissolved in
oil of lavender was thinly coated onto a metal plate or
stone; the layer hardened selectively in the light, and
was developed by the same solvent. Niépce employed
it mostly as a photoresist to make lithographic plates
for the photomechanical copying of engravings. But
upon a shiny metal plate (tin, pewter, or silver-plated
copper) a degree of tonal reversal gave an apparently
positive image, which could be enhanced by iodination.
Such a camera photograph by Niépce, dating from
1827, is in the Gernsheim Collection of the University
of Texas. A point of terminology deserves clarifying
here: although the very fi rst photographic process was
named “héliographie” by Niépce, later in the 19th cen-
tury the word “heliography” came to be widely used for
all “sun-printing,” moreover “heliographic processes”
included those intended specifi cally for reprographic
copying purposes, that is for line, rather than continu-
ous tone, images.
The Physautotype process due to Nicéphore Niépce
and Louis Daguerre (ca. 1830) was rediscovered only
recently (ca. 1995) by Jean-Louis Marignier: exposure
to light of colophony resin (abietic acid) can cause its
insolubilization, even without the presence of metallic
salts. The image on glass or shiny metal is developed
by washing, and has a subtle character when viewed
by transmitted light: its visibility depends on selective
optical scattering, rather than absorption, of the light.
The Anthotype or Phytotype process, fi rst devised
by Herschel in 1839, simply entailed the bleaching

POSITIVES: MINOR PROCESSES

by sunlight of fugitive fl ower colorants (now known

to chemistry as anthocyanins). Herschel found most

success with yellow japonica, red poppy, common

heartsease, double ten week stock, harlequin fl owers,

and purple groundsel; he crushed the fl ower petals to

pulp, extracted the expressed juices with alcohol, and

fi ltered the solutions for dyeing the paper. To bleach

the dye under an engraving, giving a positive image,

required exposures to bright sun ranging from an hour

or two for the most sensitive dyes, to several weeks for

the least. By dispersing sunlight with a prism, Herschel

performed spectrographic analyses of the responses,

which showed that a given dye was most effectively

destroyed by light of its complementary colour. Herschel

believed this positive-working process had potential for

a system of direct full-colour photography, but could

fi nd no method of fi xation, as the pictures inevitably

faded in the light.

Monochrome images were later obtained by the more

sensitive Diazotype or Feertype (Adolf Feer 1889), and

Primuline (A.G. Green, C.F. Cross, and E.J. Bevan

1890) processes, which depended on the decomposition

of diazonium salts by light. The remaining unchanged

salt—which is highly reactive—was then allowed to

couple with an organic compound included in the devel-

oper to yield an azo dye, so providing a positive-working

reprographic process in a variety of colours, determined

by the choice of the coupling agent.

Mike Ware

See also: Light-Sensitive Chemicals; Albumen Print;

Bromide Print; Daguerreotype; Gelatin Silver Print;

Photogenic Drawing Negative; Salted Paper Print;

Tintype (Ferrotype, Melainotype); Wet Collodion

Positive Processes; Liesegang, Paul Eduard; Archer,

Frederick Scott; Cased Objects; Hill, Reverend Levi

L.; Smithsonian Institution; Bayard, Hippolyte;

Talbot, William Henry Fox; Langenheim, Friedrich

and Wilhelm; Lantern Slides; Niépce de Saint-Victor,

Claude Félix Abel; Whipple, John Adams; Coloring

by Hand; Kodak; Hunt, Robert; Wothly, Jacob;

Process Inventor Year Category Image Binder & substrate

Tintype also Ferrotype Martin 1853 Silver negative Silver Collodion on black lacquered

tinplate

Transferotype Kodak Company 1888 Silver Silver Gelatin transfer to glass or canvas

Uranium print Burnett Niépce de

Saint Victor

1857

1858

Uranium Gold or Silver Paper

Uranotype Burnett 1855 Uranium Uranyl

ferrocyanide

Paper

Vanadium print Endeman 1866 Vanadium Aniline dye Paper

Vandyke see

Argentotype

Shawcross

Arndt and Troost

1889

1894

Iron Silver Paper

Wothlytype Wothly 1864 Silver and

Uranium

Silver Collodion on paper