Evening star., 1948-07-11
By Alexander J. Wedderburn
cvrotor OF Photography
The Smithsonian Institution

Inc SnifnSonI0n INSTITUTION
Although L. J. M. Daguerre of
France, inventor of the daguerreo-
type. is credited with perfecting the
first successful Photographic process,
the credit for photography as we
know it today should, perhaps, go
to an Englishman who was the first
to achieve success with the negative
method of recording an image with
light sensitive materials. He was
William Henry Fox Talbot, inventor
of the Talbotype Talbot's discovery
conceded with that of Daguerre to
the very year-1839. While both
men were working toward the same
end and the basis OF their expert
ments was the same, their ultimate
methods of Photographic reproduc-
ton were dissimilar.
Daguerre's process, which received
widespread popularity for number
of years, produced positive image
on the same plate on which the
scene was recorded. However, be-
cause of this fact, it was not possible
to make additional prints without
the tedious process of copying the
original again or by exposing a
number of plates simultaneously at
the time that the original picture
was taken. This drawback led to
the final discard of the daguerreo-
type process in favor of the one
originated by Talbot.
Prior to Talbot's discovery many
had tried and failed to record and
preserve images picked up by lens.
After several years of painstaking
experiments, Talbot overcame this
difficulty and produced the first
negative. This he obtained by coat
ing a smooth grade of writing paper
with a weak solution of salt. He
then covered one side of the sheet
with solution of silver nitrate.
When dried this paper would record
by contact printing, against the rays
of the sun, images Of leaves and
flowers. He fixed the negative by
immerSing it in strong salt solu-
ton which removed that portion of
the light sensitive silver chloride
that had not been acted upon by the
light used for exposure Strangely
enough it did not occur to Talbot at
this time that he could obtain a
positive print by transferring the
image to a second sheet of paper.
Reverse Process Found.
AS coincidence would have it, a
third investigator, Sir John Her
schel, entirely independent of both
Daguerre and Talbot, hit upon a
process similar to that of Talbot
about this same time with the eX-
ception that he perceived the ad-
vantage of making positive print
from the negative, thus reversing
the lighted and shaded areas SO
that the scene appeared as it was
in real life. Herschel is credited
with the familiar terms, positive"
and negative
Not satisfied with his basic photo
graphic process. Talbot continued
his experiments until, in 1841, he
was in a position to announce sig
nificant changes in his formulas.
Prior to this time the chemicals
used were very slow and unstable in
reaction and the new changes, part
~ his own and partly attributable
to the work of others, made the
Talbot process an important step
forward in the history OF photog-
raphy. Talbot substituted potas-
sium iodide for the common salt
that he had previously advocated
and he further added gallic acid to
the silver nitrate solution. These
changes produced a latent image,
similar to the Daguerre process,
which had to be made visible
through development. For developer
he used the same silver nitrate
eallic acid combination as was used
to sensitize the paper negative.
With the increased senSitivity of