The following article appeared in the February 1869 issue of "The
Manufacturer and Builder." (New York) Vol. 1, No. 2 (February 1869) pp.
51-52. The author of the article is named in an editorial note which
I've included at the end of the text.
- - - - - - - - - - - - -
The Daguerrean Process.
THIS most beautiful branch of the photographic art is at present
somewhat obsolete, only, however, for the reason that card photographs
are in vogue. The now, old-fashioned daguerreotype possesses a finish
which defies microscopic criticism, in vain looked for in paper
photographs, which are comparatively very coarse. In fact, as the
microscope exposes the fibres of the paper, the printed photograph
never bears microscopic inspection. Besides, the exquisite finish of
all details, and the softness, roundness, and stereoscopic effect of
the daguerreotype, constitute together a beauty which is appreciated by
the connoisseur and true lover of art.
In this article, therefore, a short exposition of the manufacture of
the daguerreotype will be given, for the additional reason that it must
be considered the best school for the future photographer to have gone
through the practice of daguerreotyping, as it not only contains the
essence of the practice of photography, but also the theory of this
fascinating occupation. Some professional photographers, who have to
pursue this business day after day, month after month, and year after
year, may not perhaps agree as to the justice of the last remark; but
the writer speaks as an amateur, to whom this occupation has a peculiar
fascination. The writer of this article will give an account of his
early and successful attempts at daguerreotyping, made in 1839 and
1840, immediately after the government of France bought Daguerre's
process, by according to him a pension for life, and gave it to the
world.
The tools were first to be procured. They consisted of a camera-
box, with meniscus lens, ground glass, and plate-holder; a few silver
plates, a box lined with glass for iodine, and another iron box
containing a few drops of mercury, with spirit-lamp fitting under it to
heat the mercury. The whole arrangement is now complete.
The camera-box is so arranged that the distance of the lens from the
ground glass is equal to the focal length of the lens, and also is
alterable, so as to be adjusted according to circumstances. The silver
plates fit in the plate-holder, also in the iodine-box, and in the
mercury-box. The first step in the operation is the cleaning of the
plates, which is begun with a piece of carded cotton, very fine pumice-
stone, and alcohol, and afterward completed with dry cotton and Paris
rouge. This cotton must be frequently substituted with fresh bits, and
care must be taken that no greasiness or other impurity of the fingers
touches the cotton at a spot which afterward comes in contact with the
silver. When thus scrupulously cleaned, the plate is placed, with the
polished side downward, on the top of the opened iodine-box, which is
kept in a dark room, and in the bottom of which has been placed some
dry iodine. In a few seconds or minutes, according to the heat of the
room and other circumstances, the vapor arising from the iodine will
have come in contact with the clean silver surface of the plate, and
combined with it to a thin film of iodide of silver. The thickness of
this film increases with the time of exposure to the iodine vapor, and
can be recognized by the color. The first thinnest film is straw
yellow; the next thicker, yellow and dark yellow; then pink, then
violet, then blue, then greenish, and finally yellow again, after which
the colors mentioned come back in about the same order, and with nearly
the same shades. But the most singular fact is, that the two yellow
shades, either the first corresponding to the thinnest film, or the
last indicating the much thicker film, are the only ones available in
this process. This last operation has to be performed in a room where
no chemical rays can penetrate, which means that it must be either
illuminated by a lamp or candle, or that the daylight must be only
admitted through red, orange, or dark yellow glass. Otherwise, the
iodized silver plate, now sensitive to light, will be affected by it.
This plate then is placed in the plate-holder and transferred to the
camera-box, which has been placed in the right position during the time
that the silver plate was exposed to the iodine vapors. This iodized
silver plate being put in exactly the same place occupied by the ground
glass, now receives the impression of the luminous image formed at that
spot by the lens, the impression received separating the combination of
iodine and silver, setting the silver free, or, in a word, resolving
the so-called iodide of silver, which was formed in the dark, into its
two constituent elements.
This action of light, in separating compounds into their elements,
takes place also in the vegetable kingdom in regard to the carbonic
acid gas contained in the atmosphere. It has been proved, in fact,
that the leaves of plants absorb this carbonic acid in the same manner
as the lungs of animals absorb the oxygen, for which reason leaves have
been called the, lungs of the plants. It has also been proved that,
under the influence of sunlight or daylight, this so-absorbed carbonic
acid is decomposed in the leaves, the oxygen escaping in its gaseous
form; while the carbon, taking on its natural solid form, is retained,
and, in combination with water, is deposited in the plant as woody
fibre. In a perfectly similar manner, in the process of
daguerreotyping, the silver is set free in the metallic state by the
influence of light in a degree proportionate to the intensity of the
light acting on different parts of the film of iodide of silver.
When such a plate is left exposed in the camera-obscura for a few
hours the image will finally appear on it by means of the silver
reduced, which, after its separation from the iodine, will appear upon
the surface of the iodized silver plate as a fine pulverulent
substance, of a different aggregate condition from the silver not so
reduced. The coating of iodide of silver must then be removed by some
kind of solution, as otherwise the decomposition of the iodide of
silver would continue every time that the plate was exposed to
daylight, and the picture, consequently, would, in the end, entirely
disappear. When, however, this sensitive coating is dissolved away,
the plate has nothing on its surface but silver in different aggregate
conditions, polished in the shadows, and pulverulent in the light; and
the picture is permanently fixed.
This was the first process of Daguerre; but as it took too long an
exposure in the camera, he attempted to shorten the time from hours to
minutes; and had the good fortune to conceive that, in the short time
of a few minutes, already a change must have taken place in the iodide
of silver film, which, notwithstanding it was invisible to the eye,
might manifest itself when the plate was exposed to the influence of
other substances. It was soon found that this silver, separated from
the iodine by the influence of light, had obtained a great affinity for
mercury, and, consequently, a strong tendency to combine with mercurial
vapors not possessed by the iodide of silver when the vapors were not
heated above 180 to 200 degrees Fahrenheit. This iodide of silver,
then, not combining with those vapors, the consequence was that, when
such a plate had been exposed to the luminous rays in the camera for a
few minutes only, and on which nothing was yet visible, exposure to
mercurial vapors of some 180 degrees Fahrenheit would not affect the
silver plate wherever it was protected by the film of iodide of silver,
but only where some silver of this film had been set free by the action
of light. The amount of deposit of mercurial vapor was also found to
be proportional to the amount of silver set free, which, again, was
proportional to the previous intensity, of the light acting on
different parts of the plate.
The deposit of mercury, or rather amalgam of mercury and silver,
thus formed on the surface of the protecting film of iodide of silver,
constituted the picture. A microscope, when of sufficient magnifying
power, detected the amalgam to consist of minute globules, very close
together in the high lights of the picture, less close in the less
illuminated portion, very sparsely distributed in the shadows, and
altogether absent in the blanks, which consisted of pure iodide of
silver.
The next operation was to remove the iodide of silver, which formed
the coating sensitive to light. Upon the removal of this, in a word,
depended the permanency of the picture, as the plate could not be
exposed to daylight without final destruction--at least great
deterioration of the impression. Fortunately, as in all problems of
the kind, substances which would readily dissolve the iodide of silver
without acting on the amalgam of silver and mercury, were at hand. One
of the best substances of this kind was found to be the hyposulphite of
soda, a strong solution of which rapidly removed the yellow coat of
iodide, leaving a clear silver surface in the shadow; the lights being
formed by the amalgam of silver and mercury in a very finely divided
form, as mentioned. The plate was then washed with distilled water and
dried by heat. This is the process as it came from the hands of
Daguerre. Successive improvements will form the subject of future
articles.
From page 344 of same issue:
ATTENTION may be directed, among other valuable articles in the
present number, to Dr. P. H. VAN DER WEYDE'S paper on the Daguerrean
Process. The paper is one of the pleasantest scientific reminiscences
ever collated in the form of a practical essay. Dr. VAN DER WEYDE is
too well known as a scientific man, both in European and American
circles, to need compliment from any source, however authoritative; and
it is somewhat in the way of self-felicitation that the proprietors of
THE MANUFACTURER AND BUILDER announce his name us that of a
contributor. Our March number will contain a capital article from his
pen, upon the Uses of Gun-Cotton.
(Van der Weyde is mentioned in "Appleton's Journal" (New York) in vol.
6, no. 130 (23 September 1871) p. 360 under the heading "Scientific
Notes" regarding a discovery in the field of spectrum analysis and the
Fraunhofer lines; and in vol. 14, no. 341 (2 October 1875) p. 446 under
the heading "Science, Invention, Discovery" regarding his effort to
challenge certain "spiritual" phenomena including "table-tumblers." --
G. W. E.)
--------------------------------------------------------------
Posted for your enjoyment. Gary W. Ewer
--------------------------------------------------------------
02-10-98 |
| |||||
 | |||||
|
