By W. M. ASHMAN.
[11] A communication to the London and Provincial Photographic
Association.
In alkaline toning with borax or acetate of soda, the first
consideration is to free the paper as much as possible from the excess
of silver nitrate remaining therein over and above the quantity used
in the production of the print; this is termed washing away the free
silver. That operation is satisfactorily performed by soaking the
prints in a few changes of clean soft water, usually four, or until the
water is no longer opalescent when tested with a few grains of salt.
The washing water so obtained is collected in the manner described to
you by Mr. F. W. Hart, and precipitated with dilute hydrochloric acid.
The vessel employed should be scrupulously clean, either earthenware,
porcelain, or wood answering the purpose.
_Experiment_ 1.--The treatment of the prints is sometimes followed
by passing them into a dilute solution of sodium acetate or ordinary
common salt, about one per cent., such as here shown, and stirring
them about for five minutes, when it will be seen they have assumed a
brick-red color, the object of which is threefold: First, the fibers
become charged with a substance which acts as a chlorine absorbent, a
necessary property to be mentioned further on. Secondly, a definite
color is insured to start with, thus obviating the possibility of
mistaking fresh prints in the toning bath for those which have become
purple by reason of the deposited gold, an important consideration when
dealing with fumed paper. Thirdly, the last trace of free nitrate of
silver is removed, thereby preventing a too rapid decomposition of the
toning bath.
Theoretically considered, it is proper that the last trace of silver
nitrate should be removed; but those who are engaged in the daily
practice of commercial work do not insist upon the strict observance
of such a rule in all cases. An especial exception is permitted and
advocated when dealing with prints from weak or underexposed negatives,
this class being found to yield richer tones by not washing any of the
free silver out.
The plan of soaking prints in a solution of sodium acetate was
originally recommended, in lieu of washing, by a member of this
Association, Mr. A. L. Henderson, as long ago as 1861, the following
being an outline of the method suggested by him: Slightly overprinted
proofs were soaked in a bath composed of
Sodium acetate 240 grains.
Water 10 ounces.
The unwashed proofs were moved about in this solution at least ten
minutes, in order to convert all the free silver nitrate into acetate
of silver. After slight rinsing in clean water the proofs were toned
with
Gold terchloride 4 grains.
Sodium acetate 240 "
Water 10 ounces.
Among the advantages claimed was an entire absence from mealiness, a
defect, you will remember, we now avoid by the adoption of ammoniacal
fuming.
Guide-books to the practice of printing usually recommended three
rapid washings; the decomposing action thus set up by the quantity of
free silver remaining in the paper materially quickens the speed of
toning. To prevent a too rapid deposition of gold some printers prefer
adding a small quantity of common salt to the toning bath, which turns
the prints sufficiently red and acts in some respects equal to an
intermediary bath.
Preserved papers--containing, as they generally do, a certain
proportion of free acid--are liable to give some trouble in toning,
owing to the retarding action of the acid present. When this occurs, it
is in a great measure overcome by the use of an intermediate bath of
an alkaline character and sufficient strength to neutralize the acid.
Either the carbonates of ammonia or soda are found useful for this
purpose, and I cannot do better than quote the one mentioned by Mr.
Frederick York, which, it will be remembered, is composed of
Washing soda 1 ounce.
Water 1 gallon.
Prints treated in the manner described are ready for toning by the
alkaline method to be dealt with later on.
This brings us to the consideration of toning baths generally. The
properties of toning baths vary somewhat according to the mode of
preparation. The term "toning," as we understand it, implies a
certain change of color brought about by chemical means, such as the
deposition of a stable metal upon one that is easily affected by the
atmosphere--electrolysis, in fact.
Evidently Mr. W. H. Fox Talbot was the first to use the toning bath
in connection with paper photography, although he does not seem to
have made much headway with his process at first; for it is recorded
that from January, 1839, the date when Mr. Talbot communicated his
discovery to the Royal Society, until 1845 very little improvement took
place. These early paper pictures, be it remembered, were designated
"photogenic drawings." Talbotype was not patented for some time
afterward.
In the year 1845, however, it was found that steeping the paper in
terchloride of gold vastly improved the results. It was not until 1853
that albumen took any part in the production of prints, the honor of
its introduction being ascribed to Mr. Henry Pollock, although it seems
that M. Le Gray, of Paris, about that time was producing stereoscopic
pictures on albumenized paper. To M. Le Gray is due the credit of
introducing gold toning in lieu of sulphur. The first toning then was
performed by the decomposition of hypo., and known as "sulphur toning,"
by which fine black tones were obtained upon the addition of an acid,
such as acetic, sulphuric, or other suitable oxidizing substance to the
hypo., gold taking no part in this process. Unfortunately, prints so
treated are said to be the least permanent of any; but of that I can
bring no actual proof, never having employed the process.
_Experiment 2.--Toning by Sulphur._--We have an unwashed silver print
here in a twenty per cent. solution of hypo., and to that we now add
a few drops of slightly dilute sulphuric acid. It will be seen that
a straw-colored substance is immediately liberated, which is sulphur
in an exceedingly fine state of division, and this becomes attached
to the print. Toning action goes on, through the silver image being
tarnished, or, more correctly, converted into sulphide of silver. This
liberation of sulphur may be expressed by the following equation:
Hypo. Sulphuric Acid
Na_{2}S_{2}O_{3} + H_{2}SO_{4} =
Glauber Salts Water Sulphur Dioxide Sulphur.
Na_{2}SO_{4} + H_{2}O + SO_{2} + S.
With respect to the reaction which takes place when toning a silver
image with sulphur, I will quote a few lines from the parent work
of reference for nearly all recent writers, namely, Hardwich's
_Photographic Chemistry_, wherein we find the following paragraph:
"It is well known that articles of silver plate become darkened by
exposure to the fumes of sulphur, or to those of sulphureted hydrogen,
of which minute traces are always present in the atmosphere. If the
stopper of a bottle of sulphureted hydrogen water be removed, and a
simply-fixed photographic positive suspended over it, the picture will
lose its characteristic red tone, and become nearly black. The black
color is even more intense than an experienced chemist would have
anticipated, because analysis teaches us that the actual quantity of
silver present in a photographic picture on paper is infinitesimally
small; and it is well known that sulphide of silver, although of a
deep brown color, approaching to black when in mass, exhibits a pale
yellow tint in thin layers, so that a mere film of silver converted
into sulphide possesses very little depth of color. To explain the
difficulty it has been suggested that the toning action of sulphur
on a red print is probably due to the production of a sub-sulphide
possessing an intense colorific power, like the sub-oxide and
sub-chloride of silver. When the toned picture is subjected to the
further action of sulphur, is converted into the ordinary protosulphide
of silver, and becomes yellow and faded."
The toning baths following the sulphur method were principally mixtures
of gold terchloride and hypo. This latter substance was found to be a
solvent of certain silver compounds by the Rev. J. B. Reade, in 1839,
Mr. Talbot having previously fixed his prints with common salt. Prints,
too, were fixed first in some cases, and toned afterward, washing
away the free silver being more or less practiced in the mixed hypo.
and gold and the sulphur toning processes. When fixing was employed
before toning, it was usual to soak washed prints in a twenty per cent.
solution of hypo. for a period of ten minutes, or until the soluble
silver salts were removed, the resulting color being a disagreeable
yellowish-brown. To improve the result so obtained the prints were
passed into a solution of--
Gold terchloride 10 grains.
Water 20 ounces.
When toning action quickly followed, the yellow color giving place to
that of a dark sepia tint. From this stage to that of mixing these
two substances together was only a natural sequence, and effected a
diminution of gold to the extent of one-fourth, as will be seen by the
following recognized formula:
Hypo. 7 ounces.
Water 20 "