From the _Photographic News_ we take the following: The use of paper coated
with a gelatino-citro-chloride emulsion in place of albumenized paper
appears to be becoming daily more common. Successful toning has generally
been the difficulty with such paper, the alkaline baths commonly in use
with albumenized having proved unsuitable for toning this paper. On the
whole, the bath that has given the best results is one containing, in
addition to gold, a small quantity of hypo and a considerable quantity of
sulphocyanide of ammonium. Such a bath tones very rapidly, and gives most
pleasing colors. It appears, moreover, to be impossible to overtone the
citro-chloro emulsion paper with it in the sense that it is possible to
overtone prints on albumenized paper with the ordinary alkaline bath. That
is to say, it is impossible to produce a slaty gray image. The result of
prolonged toning is merely an image of an engraving black color. Of this,
however, we shall say more hereafter. We wish first of all to refer to an
elaborate series of experiments by Lionel Clark on the effects of various
toning baths used with the gelatino-citro-chloride paper.
The results of these experiments we have before us at the time of writing,
and we may at once say that, from the manner in which the experiments have
been carried out and in which the results have been tabulated, Lionel
Clark's work forms a very useful contribution to our photographic
knowledge, and a contribution that will become more and more useful, the
longer the results of the experiments are kept. A number of small prints
have been prepared. Of these several--in most cases, three--have been toned
by a certain bath, and each print has been torn in two. One-half has been
treated with bichloride of mercury, so as to bleach such portion of the
image as is of silver, and finally the prints--the two halves of each being
brought close together--have been mounted in groups, each group containing
all the prints toned by a certain formula, with full information tabulated.
The only improvement we could suggest in the arrangement is that all the
prints should have been from the same negative, or from only three
negatives, so that we should have prints from the same negatives in every
group, and should the better be able to compare the results of the toning
baths. Probably, however, the indifferent light of the present season of
the year made it difficult to get a sufficiency of prints from one
negative.
The following is a description of the toning baths used and of the
appearance of the prints. We refer, in the mean time, only to those halves
that have not been treated with bichloride of mercury.
1.--Gold chloride (AuCl_{3})........... 1 gr.
Sulphocyanide of potassium......... 10 gr.
Hyposulphite of soda............... ½ gr.
Water.............................. 2 oz.
The prints are of a brilliant purple or violet color.
2.--Gold chloride...................... 1 gr.
Sulphocyanide of potassium......... 10 gr.
Hyposulphite of soda............... ½ gr.
Water.............................. 4 oz.
There is only one print, which is of a brown color, and in every way
inferior to those toned with the first bath.
3.--Gold chloride...................... 1 gr.
Sulphocyanide of potassium......... 12 gr.
Hyposulphite of soda............... ½ gr.
Water.............................. 2 oz.
The prints toned by this bath are, in our opinion, the finest of the whole.
The tone is a purple of the most brilliant and pleasing shade.
4.--Gold chloride...................... 1 gr.
Sulphocyanide of potassium......... 20 gr.
Hyposulphite of soda............... 5 gr.
Water.............................. 2 oz.
There is only one print, but it is from the same negative as one of the No.
3 group. It is very inferior to that in No. 3, the color less pleasant, and
the appearance generally as if the details of the lights had been bleached
by the large quantity either of hypo or of sulphocyanide of potassium.
5.--Gold chloride...................... 1 gr.
Sulphocyanide of potassium......... 50 gr.
Hyposulphite of soda............... ½ gr.
Water.............................. 2 oz.
Opposite to this description of formula there are no prints, but the
following is written: "These prints were completely destroyed, the
sulphocyanide of potassium (probably) dissolving off the gelatine."
6.--Gold chloride...................... 1 gr.
Sulphocyanide of potassium......... 20 gr.
Hypo............................... 5 gr.
Carbonate of soda.................. 10 gr.
Water.............................. 2 oz.
This it will be seen is the same as 4, but that the solution is rendered
alkaline with carbonate of soda. The result of the alkalinity certainly
appears to be good, the color is more pleasing than that produced by No. 4,
and there is less appearance of bleaching. It must be borne in mind in this
connection that the paper itself is strongly acid, and that, unless special
means be taken to prevent it, the toning bath is sure to be more or less
acid.
7.--Gold chloride...................... 1 gr.
Acetate of soda.................... 30 gr.
Water.............................. 2 oz.
The color of the prints toned by this bath is not exceedingly pleasing. It
is a brown tending to purple, but is not very pure or bright. The results
show, however, the possibility of toning the gelatino-chloro-citrate paper
with the ordinary acetate bath if it be only made concentrated enough.
8.--Gold chloride...................... 1 gr.
Carbonate of soda.................. 3 gr.
Water.............................. 2 oz.
Very much the same may be said of the prints toned by this bath as of those
toned by No. 7. The color is not very good, nor is the toning quite even.
This last remark applies to No. 7 batch as well as No. 8.
9.--Gold chloride...................... 1 gr.
Phosphate of soda.................. 20 gr.
Water.............................. 2 oz.
The results of this bath can best be described as purplish in color. They
are decidedly more pleasing than those of 7 or 8, but are not as good as
the best by the sulphocyanide bath.
10.--Gold chloride..................... 1 gr.
Hyposulphite of soda.............. ½ oz.
Water............................. 2 oz.
The result of this bath is a brilliant brown color, what might indeed,
perhaps, be best described as a red. Two out of the three prints are much
too dark, indicating, perhaps, that this toning bath did not have any
tendency to reduce the intensity of the image.
The general lesson taught by Clark's experiments is that the sulphocyanide
bath gives better results than any other. A certain proportion of the
ingredients--namely, that of bath No. 3--gives better results than any
other proportions tried, and about as good as any that could be hoped for.
Any of the ordinary alkaline toning baths may be used, but they all give
results inferior to those got by the sulphocyanide bath. The best of the
ordinary baths is, however, the phosphate of soda.
And now a word as to those parts of the prints which have been treated with
bichloride of mercury. The thing that strikes us as remarkable in
connection with them is that in them the image has scarcely suffered any
reduction of intensity at all. In most cases there has been a disagreeable
change of color, but it is almost entirely confined to the whites and
lighter tints, which are turned to a more or less dirty yellow. Even in the
case of the prints toned by bath No. 10, where the image is quite red, it
has suffered no appreciable reduction of intensity.
This would indicate that an unusually large proportion of the toned image
consists of gold, and this idea is confirmed by the fact that to tone a
sheet of gelatino-chloro-citrate paper requires several times as much gold
as to tone a sheet of albumenized paper. Indeed, we believe that, with the
emulsion paper, it is possible to replace the whole of the silver of the
image with gold, thereby producing a permanent print. We have already said
that the print may be left for any reasonable length of time in the toning
bath without the destruction of its appearance, and we cannot but suppose
that a very long immersion results in a complete substitution of gold for
silver.
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