Gold terchloride 5 grains.
Dissolved in water 20 ounces.
After mixing, a clear solution should result.
The _sel d'or_ process followed, and was expected to give still better
results. It was found, however, that the solutions would not keep;
and as a considerable quantity of the gold salt was needed, it caused
experimenters to search for a less expensive method. One decided point
in its favor was the circumstance that prints suffered no loss of
intensity during the operation, as they do in the case of all other
toning methods. Briefly: the prints were well washed to extract free
silver, and, after soaking five minutes in salt and water, they were
passed into an alkaline solution composed of--
Liquid ammonia 60 minims.
Water 20 ounces.
Here they became very red. After washing in clean water the surface was
flooded with a toning solution composed of
Double hyposulphite of gold and sodium (_sel d'or_) ½ grain.
Hypo 1 "
Water 1 ounce.
Upon the print assuming a purple-gray color it was withdrawn and fixed
in a sixteen per cent. solution of hypo. to dissolve the unacted upon
silver chloride. Gold, when in a fine state of subdivision, is of a
rich purple color. The layer obtained by deposition upon a silver image
is very finely divided; hence the color. The only object in continuing
the toning action beyond the stage at which a good surface color has
been reached is to obtain a deposit of sufficient density to completely
neutralize the red color of the organic silver image beneath;
therefore, it is preferable, in forming a judgment of toning action, to
examine proofs by transmitted light rather than by reflected only.
Before dealing with the various formulæ for alkaline toning I should
like to step out of the golden track to say a few words on platinum
tetracloride, PtCl_{4}.
_Experiment_ 3.--_Platinum Toning._--The value of a platinum salt as a
toning agent for silver images has been thoroughly demonstrated before
you by Mr. Henderson, when he initiated us into the secrets of ceramic
photography. My trials with this salt as a toning agent for paper
proofs have only been partially successful. By that I mean that toning
does take place when a dilute solution is employed, but the action is
too tardy for demonstration here to-night, since anything like a black
tone could not be obtained under half an hour. You will observe that
the surface becomes covered with chloride, showing the necessity for
copious washing. Yellow or discolored prints are bleached when toned
in this bath, the whites becoming very pure. The formula here given
is capable of producing a very good shade of brown in less time, and
should be permanent, since platinum is a metal practically unaffected
by the atmosphere; and I think there is good reason to suppose that
if a thin coating of platinum could be deposited on the silver image,
the protection offered would be more economical as well as stable.
Something has already been done in this direction, but not in recent
years.
The following is the composition we are now using:
Platinum tetrachloride, sirupy solution,
color of old East India sherry 5 minims.
Hydrochloric acid 150 "
Water 20 ounces.
Wash away the free silver thoroughly, warm the toning solution to 70°
Fahr., and fix in a twenty per cent. hypo. bath.
Mr. A. Watt, in the second volume of the _News_, gives a formula which
runs as follows:
Solution of platinum 30 minims.
Hypo. 3 grains.
Hydrochloric acid 5 minims.
Water 5 ounces.
This bath is said to act instantly, but I have not had an opportunity
to test it. The strength of the platinum solution here given is
indefinite, but any of our experimental members can soon ascertain the
amount of dilution necessary to obtain the most favorable results.
_Alkaline Toning._--Owing to the bleaching action which occurs in
toning silver prints with gold, which is slightly acid, certain
experiments were made, and it was found that bleaching increased in
proportion to the quantity of hydrochloric acid added. Now, in the
action of toning chlorine is disengaged, and in order to render this
powerful bleaching agent inert it has been proposed to introduce a
substance capable of combining with it, and thus, in absorbing it,
prevent undue loss of vigor. To obtain this a slightly alkaline toning
bath became a necessity, and to Mr. Waterhouse we are indebted for the
introduction of the alkaline salts (Hardwich).
Here is an example:
_Experiment_ 4.
Sodium carbonate (Na_{2}HCO_{3}) 5 grains.
Auric terchloride (AuCl_{3}) 1 grain.
Water 10 ounces.
Instead of the dry bicarbonate we will use a saturated solution. In
this as well as the following experiments we shall tone three prints of
the same subject, viz., ordinary, fumed, and preserved.
Mr. Maxwell Lyte has written on and investigated the properties of
toning solutions a great deal more than most men, and we find the
following emanating from Mr. Lyte:
Sesquichloride of gold 15 grains.
Phosphate of soda 300 "
Distilled water 1¾ pints.
And in the same communication it is mentioned that 180 grains of borax
may be substituted for the phosphate with a like result. Therefore
it will be seen that a borax toning bath is not of recent discovery,
although it does not appear to have been quoted in many formulæ for at
least a dozen years after its publication.
After the publication of Mr. Lyte's formulæ it was found that other
salts behaved similarly; and among the first suggested we found sodium
acetate, the qualities of which, extolled by the introducer, Mr.
Hannaford, have since been verified by the whole photographic world.
Here is one of the ordinary formulæ:
_Experiment_ 5.
Gold terchloride 1 grain.
Sodium acetate 10 "
" chloride 10 "
Hot water 20 ounces.
Mix twenty-four hours before use. Neutralize with chalk or whitening
(carbonate of lime).
The name of M. Le Gray must be mentioned as the originator of the lime
and gold toning bath; although the original formulæ differ somewhat
from the one now used, the results are identical. The original formulæ
consisted first in washing away a portion of the free silver by soaking
the proofs for a few minutes in two changes of water, then submitting
them to the action of an auriferous bath, composed of
Terchloride of gold, 1 per cent. solution 1 part.
Hyperchloride of lime (white powder) 3 "
Distilled water 1,000 "
The action was complete in ten to fifteen minutes, when the prints
required washing in two changes of water to free them from the chloride
of lime remaining in the fibers previous to fixing in one to six of
hypo. If the tone were satisfactory at the expiration of fifteen
minutes, the ordinary washing could be proceeded with; if not, the
proofs were submitted to a final bath composed of:
Gold terchloride 2 parts.
Hypo. 200 "
Distilled water 1,200 "
M. Le Gray says: "The proof ought not to be left in this bath less than
fifteen minutes, as that is the minimum time necessary to insure the
permanency of the picture; but it may be allowed to remain in it for as
much longer as is requisite for obtaining the desired tone." Efficient
washing in warm and cold waters completed the operation. Should any of
our provincial members experience a difficulty in obtaining calcium
chloride for their experiments, it can be easily made by causing dilute
7 to 3 hydrochloric acid to react on common whitening, and when neutral
filter and set aside for the crystals to separate out.
_Experiment_ 6.--The uranium and gold toning bath has many friends. The
tones are said to be richer and to economize gold, while it is very
easy to work. I am unable to give the author's name, but I can present
a formula which has worked well in my hands. After washing away the
free silver tone in the following mixture:
No. 1.
One grain acid solution of gold terchloride 1 ounce.
Water 7 ounces.
Neutralize with sufficient of a twenty per cent. solution of sodium
carb. (Na_{2}HCO_{3}).
No. 2.
Three grain solution of uranium nitrate 1 ounce.
Water 7 ounces.
Neutralize as in No. 1. Warm each to 70° Fahr., and mix. The bath is
then ready for use. It can be used repeatedly if desired by acidifying
with citric acid and neutralizing before use; but nothing is gained by
using it a second time.
There are methods of toning which resemble more or less those which
have occupied our attention to-night; among them may be mentioned the
tungstate bath, likewise citrate of soda. The vermilion bath, too,
might afford sufficient matter alone for a lecturette. If some one
experienced with it could be induced to bring it before us, I am sure
it would prove interesting.