_The Collodion Process._--I have been much pleased with the directions
given by DR. DIAMOND in your columns for the production of collodion
positives; but they have been hitherto unaccompanied by any reference to
the causes of those numerous failures that occur in this delicate process,
and which are so disheartening to {186} beginners. I will just enumerate a
few of the appearances with which I have been troubled, and trust that they
may elicit from other operators an account of some of their instructive
failures. I will premise, as an answer to a former Query respecting the
cost and description of lenses, that I obtained mine of Mr. Goddard, now of
Jesse Cottage, Witton, Middlesex. They are combination-lenses, two inches
and a quarter in diameter (achromatic); the front lens can be used singly
for views, producing a picture nearly seven inches square, but when
combined covering four inches. For these, with brass mounting, I paid less
than 3l.: a single lens, the same diameter, would be about 1l. They work to
focus, cover flat, and define well, producing pictures equal to the most
expensive.
I have usually preferred Mr. Archer's collodion, as the most certain and
cleanest. The silver bath is composed of thirty grains nitrate of silver
and two drops of nitric acid to each ounce of distilled water. An even film
may be obtained by the following means:--Represent the plate of glass by
the following figure:
+--------------------+
| 1 3 |
| |
| |
| 2 4 |
+--------------------+
Hold the plate with the left hand at 1, pour a body of collodion in the
centre: tilt towards 1 (being careful not to let it touch the thumb),
incline towards 2, run into 3, and pour off at 4: then hold the plate
vertically (resting the corner 4 on the neck of the collodion bottle) to
drain: incline it first to the right and then to the left, repeating this
several times until the ridges are removed. By these means an even film may
be produced, without a thick ridge, from 2 to 4. The time it may be left
before plunging into the silver bath will depend on the temperature (about
half a minute). Dip evenly into the bath, lifting up and down to allow of
the evaporation of the ether: the film will also saturate more rapidly.
When the greasy appearance is gone, it is ready for the camera. Sometimes
the film is nearly transparent and bluish, not having sufficient iodide of
silver; or it may contain too much iodide, the greater part flaking off in
the bath, leaving the collodion with very little, and that patchy; or from
being placed in the bath too quick, the lower corner still present a
reticulated appearance, which of course renders it useless.
Having exposed the plate the necessary time, the next step is the
development. The solution I usually employ is prepared with protosulphate
of iron. I do not find distilled water absolutely necessary (during the
summer months I fancied the tones were improved by using ordinary water,
perhaps from containing a little lime), and the acetate acid is not
glacial, but a description termed Beaufoy's, much less expensive. The
proportions are--
Water 2 ounces.
Acetic acid 1 drachm.
Protosulphate of iron 8 grains.
Nitric acid 2 drops.
Mix the water and acetic acid first; then dissolve the iron; and, lastly,
add the nitric acid, which, by varying the quantity, produces different
effects. On pouring the solution over the plate, there is sometimes a
difficulty experienced in causing it to flow evenly. Sometimes a little
more acetic acid in the developing solution, or, if the plate has been out
of the bath some time, redipping it, will prevent this; but if this does
not remove it, and the resulting picture is hard and unpleasant in tone, a
new bath is necessary. For positives, the resulting picture is more
pleasing and delicate by using the developing agent rather weak. After it
has remained on sufficiently long to bring out the image, the undecomposed
iodide is to be removed by hyposulphite of soda. I always use the same
solution, pouring it on and off until exhausted. Having sufficiently
washed, the picture may perhaps appear with many black spots, this may in
future be obviated by adding a little alcohol to the collodion:--or it may
be covered with white spots; in that case the collodion requires settling,
or rapidly filtrating through an old piece of loose silk. Sometimes it will
look all black and white (a common fault with collodion positives), without
middle tints: by adding a little more acetic acid, or an extra drop of
nitric acid, to the developing solution, or the addition of a few drops of
ordinary pyrogallic solution, this disagreeable effect may be overcome. In
taking portraits, it is often caused by having the sitter placed with too
much front light. Then, again, the should-be whites of the picture may be
dull and greenish by reflected, and red by transmitted, light. This effect
I generally find remedied by putting less nitric acid in the developing
solution. During the development, by watching the colour (by holding a
piece of white paper underneath), this red tendency may be observed; in
that case the drawing may be preserved by leaving the plate for about a
minute after pouring the developing agent off, and before removing the
iodide. Some change appears to take place by its contact with the air; it
gradually gets more opaque, and when finished, though not so white as many,
yet presenting an extremely rich brownish-yellow tone.
During the late dull weather, many of my plates have shown a tendency to an
uniform leaden-looking deposit, destroying the blacks of the picture. A
little more nitric acid in the bath will sometimes overcome this, but I
have not yet found a sufficient remedy. During the summer months I was in
the habit of using double the quantity of {187} iron I have stated,
diluting the solution more; then was compelled to diminish the quantity to
twelve grains, and now I use eight. I have tried the proportions
recommended by French photographers, but they seem to contain too large a
proportion of iron. I prefer the use of the protosulphate to the
protonitrate of iron from its cheapness, and the ease with which it is made
up. It will also keep for any length of time, rather improving than
otherwise.
I back with liquid jet from Suggitt, opposite the House of Correction,
Mount Pleasant, Clerkenwell. It dries rapidly, and brightens the
appearance.