_Mr. Lyte on Collodion._--When I had the pleasure of meeting you in London,
I promised that I would write to you from this place, and give you a
detailed account of my method of making the collodion, of which I left a
sample with you; but since then have been making a series of experiments,
with a view, first, to simplifying my present formulæ, and next, to produce
two collodions, one of great sensibility, the other of rather slower
action, but producing better half-tones. I have also been considering the
subject of {157} printing, and the best methods of producing those
beautiful black tints which are so much prized; and I think that, although
the processes formerly given all of them produce this effect with tolerable
certainty, yet many operators, in common with myself, have met with the
most provoking failures on this head, where they felt the most certain of
good results.
I do not pretend to make a collodion which is different in its ingredients
from that compounded by others. The only thing is that I am anxious to
define the best proportions for making it, and to give a formula which even
the most unpractised operator may work by. First, to produce the collodion
I always use the soluble paper prepared according to the method indicated
by MR. CROOKES, and to which I adverted in "N. & Q.," Vol. viii., p. 252.
Take of colourless nitric acid of 1.50, and sulphuric acid of 1.60, equal
quantities by measure, and mix them; then plunge into the mixture as much
of the best Swedish filtering paper (Papier Joseph is also very good) as
the liquid will cover; it must be placed in it a single piece at a time.
Cover the basin, and let it remain a night, or at least some hours. Then
pour off the liquid, and wash the paper till its washings cease to taste
the least acid, or to redden litmus paper. Then dry it. Of this paper I
take 180 grains to one pint of ether, and having placed them together, I
add alcohol drop by drop, till the ether begins to dissolve the paper,
which will be denoted by the paper becoming quite transparent. I have
rather increased the quantity of paper to be added, as the after treatment
rather thins the collodion. This, when shaken up and completely dissolved,
forms the collodion. To sensitize I use two preparations, one prepared with
potassium, the other with ammonium compounds; and, contrary to what many
operators find the case, I find that the potassium gives the most rapid
results. To prepare the potassium sensitizer, I take two bottles of, we
will suppose, 6 oz. each; into one of these I put about half an ounce of
iodide of potassium in fine powder, and into the other an equal quantity of
bromide of potassium, also pounded; we will call these No. 1. and No. 2. I
fill the bottle No. 1. with absolute alcohol, taking great care that there
is no oxide of amyle in it, as that seriously interferes with the action of
the collodion. After leaving the alcohol in No. 1. for two hours, or
thereabouts, constantly shaking it, let it settle, and then quite clear
decant it off into No. 2., where leave it again, with constant shaking, for
two hours, and when settled decant the clear liquid into a third bottle for
use. The oxide of amyle may be detected by taking a portion of the alcohol
between the palms of the hands, and rubbing them together, till the alcohol
evaporates, after which, should oxide of amyle be present, it will easily
be detected by its smell, which is not unlike that exhaled by a diseased
potato. Of the liquid prepared, take one part to add to every three parts
of collodion. The next, or ammonium sensitizer, is made as follows. Take
Absolute alcohol 10 oz.
Iodide of ammon. 100 grs.
Bromide of ammon. 25 grs.
Mix, and when dissolved, take one part to three of collodion, as before. I
feel certain that on a strict adherence to the correct proportion depends
all the success of photography; and as we find in the kindred process of
the daguerrotype, that if we add too much or too little of the bromine
sensitizer, we make the plate less sensitive, so in this process. When
making the first of these sensitizers, I always in each case let the
solution attain a temperature of about 60º before decanting, so as to
attain a perfectly equable compound on all occasions.
In the second, or ammonium sensitizer, the solution may be assisted by a
moderate heat, and when again cooled, may advantageously be filtered to
separate any sediment which may exist; but neither of these liquids should
ever be exposed to great cold.
I dissolve in my bath of nitrate of silver as much freshly precipitated
bromide of silver as it will take up. Next, as to the printing of positives
to obtain black tints, the only condition necessary to produce this result
is having an acid nitrate bath; whether the positive be printed on albumen
paper, or common salted paper, the result will always be the same. I have
tried various acids in the bath, viz. nitric, sulphuric, tartaric, and
acetic, and prefer the latter, as being the most manageable, and having a
high equivalent. The paper I now constantly use is common salted paper,
prepared as follows. Take
Chloride of barium 180 grs.
Chloride of ammon. 100 grs.
Chloride of potassium 140 grs.
Water 10 oz.
Mix, and pour into a dish and lay the paper on the liquid, wetting only one
side; when it has lain there for about five minutes if French paper has
been used, if English paper till it ceases to curl and falls flat on the
liquid, let it be hung up by a bent pin to dry. These salts are better than
those generally recommended, as they do not form such deliquescent salts
when decomposed as the chloride of sodium does, and for this reason I
should have even avoided the chloride of ammonium, only that it so much
assists the tints; however, in company with the other salts, the nitrate of
ammon. formed does not much take up the atmospheric moisture, and I have
never found it stain an even unvarnished negative. To sensitize this paper
take
Nitrate of silver 500 grs.
Acetic acid, glacial 2 drs.
Water 5 oz.
Mix, and lay the paper on this solution for not less than five minutes, and
if English paper, double that time. The hyposulphite to be used may be a
very strong solution of twenty to twenty-five per cent., and this mode of
treatment will always be found to produce fine tints. After some time it
will be found that the nitrate bath will lose its acidity, and a drachm of
acetic acid may be again added, when the prints begin to take a red tone:
this will again restore the blacks. Lastly, the bath may of itself get too
weak, and then it will be best to place it on one side, and recover the
silver by any of the usual methods, and make a new bath. One word about the
addition of the bromide of {158} silver to the double iodide, as
recommended by DR. DIAMOND. I tried this, and feel most confident that it
produces no difference; as soon as the bromide of silver comes in contact
with the iodide of potassium, double decomposition ensues, and iodide of
silver is formed. Indeed, farther, this very double decomposition, or a
similar one, is the basis of a patent I have just taken for at the same
time refining silver and manufacturing iodide of potassium; a process by
which I much hope the enormous present price of iodide of potassium will be
much lowered.