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.

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.

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.

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.

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.