TONING THE PRINT.
If a print on albumenized paper be fixed without any intermediate
process, the result is that the image is of a red, disagreeable tone,
and unsightly. Moreover, it will be found that, if such a print be
exposed to the atmosphere, it rapidly loses its freshness, and fades. In
order to avoid this unsightliness, resort is had to toning, the toning,
in reality, being the substitution of some less attackable metal for
the metallic silver which forms a portion of the print. The usual metal
used for substitution is gold applied in the state of the ter-chloride.
It is not very easy to tell precisely how the substitution is effected;
the question is, at present, sub judice, and, therefore, we propose
to omit any theory that may have been broached. It is sufficient to
say that it is believed the first step towards the reduction of the
gold is the production of a hydrated oxide, and never metallic gold.
Be that as it may, if a finely-divided silver be placed in a solution
of chloride of gold, the silver becomes converted into the chloride,
and the gold is quickly reduced to the metallic state; and since gold
combines with more chloride than does silver, it is manifest that when
the substitution takes place,[25] the metallic gold deposited must
be very much less than the silver. The colouring power of gold is,
however, very great, when in the fine state of division in which we have
it, being an intense purple to blue colour, and a very little of this
mixed visually with the ruddy or brown colour of the albuminate which
has been discoloured by light gives, after fixing, a pleasing tone. A
picture, when toned thus, is composed of silver subchloride, metallic
gold, and an organic compound of silver. If a print be kept in the
toning bath too long, we are all aware that the image becomes blue and
feeble, and the same disaster happens when a toning bath is too strong,
_i.e._, is too rich in gold solution. The reason of this is, that too
much gold is substituted for the silver in the sub-chloride, and there
is in consequence too great a colour of the finely-precipitated gold
seen. To make a toning bath, the first thing is to look after the gold.
There is a good deal of chloride of gold sold, which is, in reality, not
chloride of gold, but a double chloride of gold and of some such other
base as potassium, and if it be paid for as pure chloride of gold, it
is manifest that the price will be excessive. It is best to purchase
pure chloride of gold, though it may be slightly acid, since subsequent
operations correct the acidity. In our own practice we get fifteen-grain
tubes, and break them open, and add to each grain one drachm of water,
and in this state it is convenient to measure out. Thus, for every grain
of gold to be used, it is only necessary to measure out one drachm
into a measure. In delicate chemical operations, this would rightly
be considered a rough method; but for a practical photographer it is
sufficiently precise.
Now if chloride of gold alone were used, it would be found that the
prints, after immersion in a dilute solution, were poor and "measley,"
and practice has told us that we must add something to the solution to
enable it to act gradually and evenly. First of all, the gold solution
must be perfectly neutral, and we know no better plan than adding to it
a little powdered chalk, which at once neutralizes any free acid. It
is not a matter of indifference what further retarder is added, for
the reason that the more you retard the action, the more ruby-coloured
becomes the gold, and less blue. A well-known experiment is to dissolve
a little phosphorus in ether, and add it to a gallon of water, and then
to drop in and stir about half a grain of chloride of gold. Phosphorus
reduces the gold into the metallic state, but when so dilute the
reduction takes place very slowly. The gold will, however, precipitate
gradually, but it will be in such a fine state of division that it is
a bright ruby colour. A very common addition to make to a toning bath
is acetate of soda, and if the gold be in defect, the same appearance
will take place in the solution. If chloride of lime, however, be added
instead, and a commencement of precipitation of gold be brought about,
the gold will be of a blue colour, having a slight tendency to purple.
In this case, the grains of gold deposited are larger than when it is in
the ruby state. The tone of the print then depends in a large measure
on the degree of rapidity with which the gold is deposited. The quicker
the deposit, the larger and bluer the gold, whilst an extremely slow
deposition will give the red form. It often happens that no matter how
long a print is immersed in a toning bath, it never takes a blue tone.
The reason will be obvious from the above remarks.
We now give some toning baths which are much used.
No. 1.--Gold tri-chloride 1 grain
Sodium carbonate 10 grains
Water 10 ounces
This bath must be used immediately after mixing, since the gold is
precipitated by the carbonate. The tones given by this bath are purple
and black. The prints should be toned to dark brown for the purple tone,
and a slightly blue tone for the black tone.
No. 2.--Gold tri-chloride 2 grains
Saturated solution
of chloride of
lime 2 drops
Chalk a pinch
Water 16 ounces
The saturated solution of chloride of lime is made by taking the common
disinfecting powder, and shaking a teaspoonful up in a pint bottle.
When the solids have settled, the clear liquid can be decanted off, and
corked up till required. This is the solution used above. It is as well
to keep this solution in the dark room.
The water with this bath should be hot (boiling better still), and the
bath may be used when it is thoroughly cool. It is better, however, to
keep it a day before using, since, when fresh, the action is apt to
be too violent, and the prints are readily over-toned. The tone with
this bath is a deep sepia to black. To get the first tone a very short
immersion is necessary; the prints should be almost red. For a black
tone the prints should be left in the solution till they are induced to
be of a purple hue.
No. 3 is made as follows:--
Sodium acetate 1 drachm
Gold trichloride 5 minim
Distilled water 12 ounces
This bath is a most excellent one in many respects, and should not be
used under a week to get the best result. As this is a long time to keep
a bath, it is as well to have two always on stock. It keeps indefinitely
if proper care be taken of it. This produces a purple or brown tone,
according to the length of time the print is immersed in it.
Now, as to toning the print. After the day's printing is done, the
prints should be placed in a pan of good fresh water, in order to
dissolve out all or a certain amount of silver nitrate that is
invariably left in them. A puncheon, such as is used in dairies, is
very convenient. It should be filled with water, and the prints placed
in one by one, taking care that no one sticks to its neighbour, as this
would be a fruitful source of unequal toning. Most water contains a
little carbonate of lime and chloride of sodium, &c.; the water will
therefore become milky. When the prints have been in the first water
for ten minutes, they should be removed to another vessel of water, one
by one. The first wash water should be placed in a wooden tub, with
a tap let into it about six inches above the base, together with a
little common salt. The salt forms chloride of silver, which gradually
precipitates, and the clear water is then drawn off on the next day, and
the sediment is left undisturbed.
[Illustration: _Fig._ 27.]
It now remains to see which toning bath is to be used. If No. 1 or 3,
the whole of the free silver should as far as possible be washed away,
which may entail three or four changes of water; the last two washings
it will hardly repay to place in the tub; the second washing should
certainly be added to it. If No. 2 toning bath be used, a little free
silver should remain in the print; in fact, the washing should be
confined to two changes of water.
When toning operations are commenced, the toning solution is poured
off from any sediment that may be in the bottle containing it into a
dish a couple of inches wider each way than the largest print which
has to be toned. If big prints have to be toned, it is inadvisable to
place more than a couple in the dish at the same time, since there is a
certain awkwardness in judging of the amount of tone given to a print
which is (say) between two or three. The prints should be placed face up
in the solution, and great care should be taken that liquid separates
each print from the next one to it, otherwise there will be patches of
unequal toning. The dish containing the prints in the solution should be
gently rocked to secure a proper mixture of the solution which may have
been robbed of its gold in those strata next surface of the prints. The
rocking is also advisable to cause any adhesion between two deep-toning
prints impossible. If the prints be of small size, a dozen or more may
be toned at one operation. Each print should be frequently brought to
the surface of the liquid, and examined in order to see how the toning
action is progressing. When one print is judged sufficiently toned, it
is removed to a dish containing pure water, and another untoned print
placed in the dish in its stead. This operation is continued till all
the prints are toned. We have heard that it has been suggested to place
the prints in water containing a little acetic acid or common salt, in
order to stop the toning action continuing from the solution which may
be held in the paper. The former is most undesirable, acetic acid, as we
shall see presently, decomposing the fixing bath.
As to the addition of common salt, we can scarcely give a favourable
opinion regarding it. The addition of a chloride does, in truth, alter
the colour of the deposited gold (see _ante_), and it may be this that
gives rise to the opinion that it corrects toning action. Of one thing
we have little doubt, however, and that is, that the addition of any
large amount of common salt will tend to turn the albumenate of silver
into chloride, which in fixing will materially weaken the print. When
giving the formula of the toning baths, we have indicated the depth to
which toning should take place. One great point to attend to is, that
a print should not be a slatey colour when fixed, and that can only
be avoided by stopping the toning action when the print arrives at a
blue-purple stage.
The toning bath, when used, should be replaced in the bottle, and we
recommend that it be kept in a dark place, otherwise any chloride of
silver which finds its way into the solution will darken and be a
nucleus for the precipitation of gold from the solution. The energy of
the toning bath would, in consequence, be wholly gone. It will be found
that in very cold solutions formed in winter the toning action is much
slower than in summer, and we need scarcely point out that this due to
the fact that cold invariably retards chemical action. This retardation
is not advantageous, and it will be found positively hurtful as to the
colour of the precipitated gold. We therefore recommend that the toning
solution and the dish in which it is to be poured should be warmed
before the fire, the former to a temperature of about 70°F., and the
latter a little higher. By this means the toning action will take place
as rapidly as in warm weather, and the same tones be produced. It must
be remembered we are writing for all; not for those alone who have
an elaborate arrangement for keeping their operating rooms at a good
temperature in all weathers, but also for those who cannot afford the
luxury. It is for this reason that we have given the above directions.