Scientific American Supplement, No. 623, December 10, 1887Various
Science
Scientific American Supplement, No. 623, December 10, 1887
Various
Science -- Periodicals
Now, having come (rightly, I think, you will admit) to the conclusion
that films have these advantages, you naturally ask, What are their
disadvantages? Remembering, then, that I am only advocating stripping
films, I consider they have but two disadvantages: First, they entail
some additional outlay in the way of apparatus, etc. Second, they are
a little more trouble to finish than the glass negatives, which sink
into insignificance when the manifold advantages are considered.
In order to deal effectively with the second objection I mentioned,
viz., the extra trouble and perseverance, I propose, with your
permission, to carry a negative through the different stages from
exposure to completion, and in so doing I shall endeavor to make the
process clear to you, and hope to enlist your attention.
The developer I use is slightly different to that of the Eastman
company, and is as follows:
A.
Sulphite of soda. 4 ounces.
To be dissolved in 8 ounces of hot distilled water, then rendered
slightly acid with citric acid, then add--
Pyrogallic acid. 1 ounce.
Water to make up to 10 ounces.
B.
Pure carbonate of soda. 1 ounce.
Water to make up in all to 10 ounces.
C.
Pure carbonate of potash. 1 ounce.
Water to make up to 10 ounces.
D.
Bromide of potassium. 1 ounce.
Water to make up to 10 ounces.
I have here two half-plate films exposed at 8:30 A.M. to-day, one with
five and one with six seconds' exposure, subject chiefly middle
distance. I take 90 minims A, 10 minims D, and 90 minims B, and make
up to 2 ounces water. I do not soak the films in water. There is no
need for it. In fact, it is prejudicial to do so. I place the films
face uppermost in the dish, and pour on the developer on the center of
the films. You will observe they lie perfectly flat, and are free from
air bubbles. Rock the dish continually during development, and when
the high lights are out add from 10 to 90 minims C, and finish
development and fix. The negatives being complete, I ask you to
observe that both are of equal quality, proving the latitude of
exposure permissible.
I now coat a piece of glass half an inch larger all round than the
negative with India rubber solution (see Eastman formula), and
squeegee the negative face downward upon the rubber, interposing a
sheet of blotting paper and oilskin between the negative and squeegee
to prevent injury to the exposed rubber surface, and then place the
negative under pressure with blotting paper interposed until
moderately dry only.
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