[Footnote: A communication to the Photographic Society of Ireland.]
Few of those who work with gelatine dry plates seem to be aware of the
great beauty of the transparencies for lantern or other uses which can
be made from them by ferrous oxalate development with the greatest ease
and certainty.
I think this a very great pity, for I hold the opinion that the lantern
furnishes the most enjoyable and, in some cases, the most perfect of all
means of showing good photographic pictures. Many prints from excellent
negatives which may be passed over in an album without provoking a
remark will, if printed as transparencies and thrown on the screen, call
forth expressions of the warmest admiration; and justly so, for no
paper print can do that full justice to a really good negative which a
transparency does. This difference is more conspicuous in these days of
dry gelatine plates and handy photographic apparatus, when many of our
most interesting negatives are taken on quarter or 5 x 4 plates the
small size of which frequently involves a crowding of detail, much of
which will be invisible in a paper print, but which, when unraveled or
opened out, as it were, by means of the lantern, enhances the beauty of
the pictures immensely.
When I last had the pleasure of bringing this subject before the members
of our society, it may be remembered that I demonstrated the ease
and simplicity with which those beautiful results maybe obtained, by
printing in an ordinary printing frame by the light of my petroleum
developing lamp, raising one of its panes of ruby glass for the purpose
for five seconds, and then developing by ferrous oxalate until I got the
amount of intensity requisite. On that evening, in the course of a very
just criticism by one of our members, Mr. J. V. Robinson, he pointed out
what was undoubtedly a defect, viz., a slightly opalescent veiling of
the high lights, which should range from absolutely bare glass in the
highest points. He showed that, in consequence of this veiling, the
light was sensibly diminished all over the picture. This veiling of the
high lights was a serious disadvantage in another important particular,
inasmuch as it lessened the contrast between the lights and shadows of
the picture, thereby robbing it of some of its charm and deteriorating
its quality.
Since that evening I have endeavored, by a series of experiments, to
find out some means by which this opalescence might be got rid of in the
most convenient manner. Cementing the transparency to a piece of plain,
clear glass with Canada balsam, as suggested by Mr. Woodworth, I found
in practice to be open to two formidable objections. One of these was
that Canada balsam used in this manner is a sticky, unpleasant substance
to meddle with, and takes a long time--nearly a month--to harden when
confined between plates in this manner. The other objection was of
extreme importance, namely, that, in consequence of commercial gelatine
plates not being prepared on perfectly flat glasses in all cases, I
found that, after squeezing out the superfluous balsam and the air
bubbles that might have formed from between the two plates, they are
liable to separate at the places where the transparency is not flat,
causing air bubbles to creep in from the edges, as you may see from
these examples. I, therefore, have discarded this method, although it
had the effect desired when successfully done.
I have hit, however, upon another way of utilizing Canada balsam, which,
while retaining all the good qualities of the former method, is not
subject to any of its disadvantages. This consists in diluting the
balsam with an equal bulk of turpentine, and using it as a varnish,
pouring it on like collodion, flowing it toward each corner, and pouring
it off into the bottle from the last corner, avoiding crapy lines by
slowly tilting the plate, as in varnishing. If the plate be warmed
previously, the varnish flows more freely and leaves a thinner coating
of balsam behind on the transparency. When the plate has ceased to drip,
place it in a plate drainer, with the corner you poured from lowest, and
leave it where dust cannot get at it for four or five days, when it will
be found sufficiently hard to be put into a plate box. The transparency
may be finished at any time afterward by putting a clean glass of the
same size along with it, placing one of the blank paper masks sold
for the purpose--either circular or cushion-shaped to suit the
subject--between the plates, and pasting narrow strips of thin black
paper over the edges to bind them together. This method is very
successful, as you may see from the examples. It renders the high lights
perfectly clear, and leaves a film like glass over all the parts of the
transparency where the varnish has flowed.
In order to avoid the risk of dust involved in this process, I tried
other means of arriving at similar results and with success, for the
plates I now submit to you have been simply rubbed or polished, as I
may say, with a mixture of one part of Canada balsam to three parts of
turpentine, using either a small tuft of French wadding or a small piece
of soft rag for the purpose, continuing the rubbing until the plate is
polished nearly dry. This method is particularly successful, rendering
the clear parts of the sky like bare glass. I have here a plate which is
heavily veiled--almost fogged, in fact--one half of which I have treated
in this way, showing that the half so treated is beautifully clear,
while the other half is so veiled as to be apparently useless.
I have tried to still further simplify this necessary clearing of those
plates, and find that soaking tor twelve hours in a saturated solution
of alum, after washing the hypo out of the plate, is successful in a
large number of cases; and where it is successful there is no further
trouble with the transparency, except to mount it after it becomes dry.
Where it is not entirely successful I put the plate into a solution of
citric acid, four ounces to a pint of water, for about one minute, and
have in nearly all cases succeeded in getting a beautifully-clear plate.
The picture must not be left long in the citric acid solution, or it
will float off; neither do I like using citric acid until after trying
the alum, for a similar reason.
I may mention that I recommend a short exposure in the printing-frame
and slow development, in order to get sufficient intensity. Of course
the exposure is always made to a gas or petroleum light. I also still
prefer the old method of making the ferrous oxalate solution, pouring
it back into the bottle each time after using, and using it for two
or three months, keeping the bottle full from a stock bottle, and
occasionally putting a little dry ferrous oxalate into the bottle and
shaking it up, allowing it to settle before using next time. By treating
it in this way it retains its power fairly well for a long time; and as
it becomes less active I give a little longer exposure, balancing
one against the other. Making the ferrous oxalate solution from two
saturated solutions of iron sulphate and potassium oxalate has not
succeeded so well with me for transparencies. The tone of the picture is
not so black as when developed by the old method; and I do not like gray
transparencies for the lantern. I also recommend very slow gelatine
plates, about twice as sensitive as wet collodion--not more, if I can
help it.
I have demonstrated, I hope to your satisfaction, the possibility of
producing lantern slides from commercial gelatine plates of a most
beautiful quality--ranging from clear glass to deep black, and
giving charming gradation of tones, showing on the screen a film as
structureless as albumen slides, without the great trouble involved in
making them. You must not accept the slides put before you this evening
as the best that can be done with gelatine. Far from it; they are only
the work of an amateur with very little leisure now to devote to their
manufacture, and are merely the result of a series of experiments which,
so far as they have gone, I now place before you.--_Thomas Mayne, T. C.,
in British Journal of Photography._
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