1155
feature that the silver image was bleached by mercuric
chloride, converting it to silver chloride and mercurous
chloride, so whitening the deposit in the highlights. The
Pannotype of Wulff and Company (1853) is another
variation on Ambrotype, backed by black waxed linen,
or leather, rather than paper.
The Hillotype enjoys a notorious history: it was
claimed in 1850 to be a natural colour version of the Da-
guerreotype, and the life of its inventor, Levi Hill, reads
no less colourfully. Although denounced as fakes by
jealous daguerreotypists of the day, there are specimens
of original Hillotypes in the Smithsonian Institution.
Hill’s chemically bizarre procedure is complicated and
dangerous, but was carefully replicated in 1985 by Jo-
seph Boudreau, who succeeded in obtaining Hillotypes
showing some vestiges of “natural colour.”
The fi rst Direct positive silver photographs were
created in 1839 by Hippolyte Bayard, who used his
unnamed positive-working process directly in the
camera with considerable success. In 1840, Henry
Talbot devised a similar “positive photogenic drawing
paper” which he called Leucotype: an ordinary salted
silver paper was heavily exposed and fi xed, to provide
a uniform, black ground of silver; treatment with strong
potassium iodide solution rendered this layer susceptible
to bleaching by light, which formed pale yellow silver
iodide. Such photographs tend to fade in the light, and
are very rare.
With their Hyalotype of 1849 the brothers Friedrich
and Wilhelm Langenheim provided the earliest lantern
slides as silver-albumen positive transparencies (diapos-
itives) on glass, using the Niépceotype process of 1847
due to Claude Felix Abel Niépce de Saint Victor. Other
variations bearing names suggestive of a glass substrate
were: John Whipple’s Crystalotype of 1854, and the
Opalotype publicised by P.C. Duchochois in 1865 using
translucent opal glass. The Crystoleum process of 1880
involved glueing an albumen positive face down onto a
concave glass surface, removing much of the backing,
and colouring by hand in oils. Such manual embellish-
ment featured in other named processes: Wilson’s Sen-
notype of 1864 was a hand-coloured albumen positive
on glass; Urie’s Relievotype of 1854 was a collodion
positive on glass with the background scraped away,
and re-backed with a painted card; it was introduced by
Thomas Lawrence in 1857.
A wider range of substrates was made possible in
1888 by the Kodak Company’s Transferotype, which
was a “stripping emulsion” whereby the silver-gelatin
image could be transferred onto glass or canvas, for
example. Prints on genuine ivory are rare; Ivorytype
(John Mayall 1855) and Eburneum prints (John Burgess
1865) were imitations on specially-whitened substitutes.
To make satisfactory photographic images on enamels
and ceramics which had to be fi red at high temperatures
under a glaze, the Photoceramic process due to Pierre
Michel Lafon de Camarsac in 1855 used chemical toning
to replace the silver by a more refractory noble metal,
such as gold, platinum, or iridium. Other photoceramic
techniques employed refractory pigments applied by the
carbon process (see below).
Some silver sensitizers incorporated novel chemical
constituents. Robert Hunt added succinic acid in his
Energiatype process of 1844: a paper that could either be
printed-out, or developed (with ferrous sulphate, causing
Hunt to re-name this process “Ferrotype”—not to be
confused with the alternative name for Tintype.) Jacob
Wothly included uranium salts in a silver emulsion in his
eponymous Wothlytype of 1864. Extravagant claims for
this print-out process (sometimes misleadingly called
Uranotype) attracted attention initially, but its virtues
were soon discounted; it did however represent the fi rst
use of collodion as a binding agent.Iron Carboxylate Processes
The “ferric” processes—collectively called ‘siderotypes’
by Sir John Herschel—are based upon light-sensitive
salts of iron(III) with “vegetable acids” such as citric,
tartaric and oxalic, which are polycarboxylic acids.
The photochemistry is described under light-sensitive
chemicals, and under Cyanotype and Platinum Print—
the two major nineteenth-century iron-based printing
processes. Besides these two, there were more than a
dozen minor siderotype processes, both positive- and
negative-working, which furnished images in a variety
of substances.
Henri Pellet’s process of 1877, called Cyanofer in
France, produced Prussian blue prints, but differed from
the simple cyanotype in being positive-working. A ver-
sion of the sensitizer due to Giuseppe Pizzighelli and
Ludwig von Itterheim contained a mixture of iron(III)
chloride, tartaric acid, and gum Arabic: the gum was
hardened by the iron(III) salt, but where light fell this
was reduced to iron(II), allowing the gum to re-soften.
A developer of potassium ferrocyanide formed Prussian
blue in the insoluble, unexposed regions and, to fi x the
image, the Prussian white formed in the soluble, exposed
regions was washed away. The Pellet process was re-
puted to be diffi cult to work satisfactorily—highlights
were often blued—but it found some application for
copying purposes, for instance reproducing maps for
the Survey of India Offi ce. Alphonse Poitevin’s process
of 1860 had a commonality with Pellet’s: it was also
positive-working, and relied on the ability of iron(III)
chloride to harden a colloid, in this case gelatin carrying
a pigment. In regions where the light caused reduction
of iron(III) to iron(II), the gelatin re-softened, and was
washed away in the development bath with its attendant
pigment. Also based on cyanotype were John Mercer’s