HF The History of Photography 600pág

16 The introduction of photography on glass
THE ALBUMEN PROCESS I 848-c. I 8 57
It is surprising that the first practical photographic process on glass was introduced
as late as 1848, for glass had the advantage of being a cheaper base for the sensitive
coating than a silvered copper plate, as well as being free from the defects which
marred the paper processes. Its transparency made it the perfect base for the multiplication
of copies, and but for its weight and fragility it would have established itself
as the ideal carrier of photographic emulsions. The chief problem in devising a
practical process on glass was to find a vehicle for the silver salts which would not
dissolve or float off during development, fixing, and rinsing.
The use of glass for photographic purposes was not novel. It will be remembered
that Nicephore Niepce had used it for two views before 1829, and Daguerre also
made some 'sketches upon glass' which he considered to have 'more charm, and,
above all, much greater delicacy' than pictures on metal. However, he failed to speed
up Niepce's bitumen process.
SIR JOHN HERSCHEL evolved a glass process in September 1839 (see page 97), and
ROBERT HUNT and his friend John T. Towson of Falmouth experimented with this
method, which 'is capable of producing pictures of the most extreme delicacy and as
we are enabled to take a number of positive copies from an original negative photograph
on glass, it is a means which promises to be exceedingly valuable in forwarding
the most important branch of the photographic art, namely publication' .1 Yet in
spite of Hunt's opinion, Herschel's glass process must for some reason or other have
been impracticable; otherwise it is difficult to understand why it should have failed
to win immediate popularity, for a good alternative to the calotype would have
rendered photographers independent of Talbot's patents. (Positive copies could have
been printed on Photogenic Drawing Paper, which was not patented.)
Undeterred by these apparent failures, ABEL NIEPCE DE SAINT-VICTOR, a cousin
of Nicephore Niepce, continued to experiment with glass, and found eventually,
after having tried starch and gelatine, that white of egg (albumen) acted as a satisfactory
coating. He communicated his discovery to the Academie des Sciences on
25 October I847,2 but details of manipulation were not published until 12June of the
following year.3
In the albumen process the glass plate was coated with a thin layer of white of egg
containing a few drops of a solution of iodide of potassium. When dry, the plate was
washed with an acid solution of nitrate of silver, and after exposure the latent image
was developed with gallic acid, and fixed in the usual way.