THE PHOTOGRAPHIC JOURNAL. January 1, 1859
Mr. HARDWICH has communicated to the Photographic Society of London some observations on photographic printing, in which he deprecates, as unjust, the prevalent disposition to decry the methods of toning and fixing now in use. In skilful hands, doubtless, the methods in vogue are fully adequate to secure permanency. but the host of pictures "fading away" that meet us on every hand, prove too forcibly that some radical defect exists, if not in the formula at least in the manipulation. It is better to seek to improve the former than the latter; therefore Mr. Hardwich proposes an improved toning by alkaline chloride of gold. This mode of toning is adapted for any kind of sensitive paper, but its peculiar value is seen in the case of albumenized paper, which is sometimes difficult to colour by the sel d'or process, and even in the ordinary fixing and toning bath of hyposulphite of soda and gold, does not attain to an agreeable tone, unless the bath be kept in a very active condition. Make a solution of chloride of gold, one grain to the ounce of water; take of this
|Solution of chloride of gold||1 fluid drachm.|
|Sesquicarbonate of soda.||1 drachm.|
|Citric acid||20 grains.|
|Water (pure)||12 fluid ounces.|
This solution will not keep when mixed, as it gradually undergoes a change, becoming colourless, and toning more slowly. It is not clearly understood what part the citric acid plays in this mixture; in a warm alkaline solution of chloride of gold it throws down an indigo blue deposit of metallic gold.
A strongly albumenized paper is to be preferred for this method, especially one that prints rather red, otherwise the gold is liable to yield too blue a colour. A rich velvety appearance is promoted by using a sensitizing bath of full strength: sixty grains of silver to the ounce for a paper salted with a ten grain salting solution.
The prints may be kept for a few hours after removal from the printing fame, but it is best to tone them at once. Wash them in two or three changes of water until milkiness disappears; they may be left in the water until it is convenient to tone them, which is done as follows
Mix the ingredients of the formula given above in an evaporating dish, and when effervescence ceases, place a spirit-lamp beneath, and raise the temperature, with constant stirring, to about 120° F., which is indicated by the steam beginning to rise, and a bluish discolouration, due to commencing reduction, is seen. The lamp must now be removed, else much of the gold will be reduced, changing the colour of the fluid to an inky black, after which it will be nearly useless. Filtering is unnecessary.
This warm liquid is poured into a flat dish, and the prints are put into it, two or three at a time. A little discolouration of the toning solution may be disregarded, since it is caused by a quantity of gold quite microscopic, and will not injure the whites of the proof. Keep the prints constantly moving, and watch the changes of colour. The first two or three may perhaps be toned in about five minutes; but as the liquid cools down, and the quantity of gold decreases, twenty minutes or longer may be allowed. The tune, however, is greatly influenced by the quality of the paper; English papers strongly albumenized requiring a longer action.
It the prints are removed from the toning bath as soon as the blue colour of the gold is seen, they will generally change in the fixing bath to a warm hue of brown; but when left for two or three minutes longer, the deeper tone acquired is permanent. The proofs are ready for fixing when they cease to appear red by transmitted light. Over-printed proofs yield the blackest colours, because they may be kept in the gold a longer time without losing the half tones. It is not advisable to attempt to obtain pure white and black tones on proofs printed from feeble negatives, for unless there be a perceptible amount of bronzing, the deep blacks cannot be obtained on albumenized paper.
Each grain of chloride of gold ought to tone six or seven prints, 5 X 7, and two or three of 10 X 12, which is rather more than the number yielded by the same quantity of gold in the sel d'or process.
Fixing--The proofs must be rinsed on both sides upon removal from the gold bath, ant fixed in the following solution
|Hyposulphite of soda||6 ounces.|
|Carbonate of soda||½ ounce.|
This solution will keep many weeks, and imparts a slightly improved colour after being much used. The carbonate of soda is added to prevent the fixing solution from acquiring sulphurtoning properties to an injurious extent. The time of immersion is from ten to fifteen minutes, or until no mottling appears in the proof when held against the light. The proofs are washed in the usual way.