It was announced that the inventor of the Daguerreotype had succeeded in improving the sensibility of his plates to such an extent, as to render an instantaneous exposure sufficient for the production of the best effects; consequently, securing faithful impressions of moving obj ects. In a communication with which I was favoured from M. Daguerre, he said,—"Though the principle of my new discovery is certain, I am determined not to publish it before I have succeeded in making the execution of it as easy to everybody as it is to myself. I have announced it immediately at the Royal Academy of Paris, merely to take date, and to ascertain my right to the priority of the invention. By means of that new process, it shall be possible to fix the images of objects in motion, such as public ceremonies, marketplaces covered with people, cattle, etc.—the effect being instantaneous"
In 1844, M. Daguerre, in a letter to M. Arago, published this process; but it proved so complex in its manipulatory details, and so very uncertain, that it has not been adopted. As it is, however, curious, and involves the use of some agents not ordinarily employed, it is thought advisable to make some extracts from the Comptes Rendus for April, 1844, in which it was published :—
" By superposing on the plate several metals, reducing them to powder by friction, and by acidulating the empty spaces which the molecules leave, I have been enabled to develope galvanic actions which permit the employment of a much thicker layer of iodide, without having to fear, during the operation of light in the camera obscura, the influence of the liberated iodine.
" The new combination which I employ, and which is composed of several metallic iodides, has the advantage of giving a sensible layer capable of receiving impressions simultaneously by all the degrees of tone, and I thus obtain, in a very short space of time, the representation of objects vividly enlightened with demi-tints, all of which retain, as in nature, their transparency and their relative value.
"By adding gold to the metals which I first used, I am enabled to avoid the great difficulty which the use of bromine, as an accelerating substance, presented. It is known that only very experienced persons could employ bromine with success, and that they were able to obtain the maximum of sensibility only by chance, since it is impossible to determine this point very precisely, and since immediately beyond it the bromine attacks the silver, and is opposed to the formation of the image.
" With my new means, the layer of iodine is always saturated with bromine, since the plate may, without inconvenience, be left exposed to the vapour of this substance for at least half the necessary time; for the application of the layer of gold is opposed to the formation of what is called the veil of bromine. The process which I am about to give may, perhaps, be found rather complicated; but, notwithstanding my desire to simplify it as much as possible, I have been led, on the contrary, by the results of my experiment, to multiply the substances employed, all of which play an important part in the whole process. I regard them all as necessary for obtaining a complete result, which must be the case, since I have only gradually arrived at discovering the properties of these different metals, one of which aids in promptitude, the other in the vigour of the impression, etc.
" The operation is divided into two principal parts : the first, which is the longest, may be made a long time previously, and may be regarded as the completion of the manufacture of the plate. This operation, being once made, serves indefinitely ; and, without recommencing it, a great number of impressions may be made on the same plate. The new substances employed are :Aqueous solution of bichloride of mercury: solution of cyanide of mercury: white oil of petroleum, acidulated with nitric acid : solution of chlorine of gold and platinum. These are prepared as follows:
8 grains of bichloride of mercury in 10,000 grains of distilled water.
A flask of distilled water is saturated with cyanide of mercury, and a certain quantity is decanted, which is diluted with an equal quantity of distilled water.
This oil is acidulated by mixing with it one-tenth of pure nitric acid, leaving it for at I have given the preference to this oil over the fixed oils, because it always remains limpid, although strongly acidulated. My object in employing an least forty-eight hours, occasionally agitating the flask. The oil which is acidulated, and which then powerfully reddens litmus-paper, is decanted. It is also a little coloured, but remains very limpid.
* The most suitable oil of petroleum is of a greenish yellow tint, and takes, at different angles, azure reflections.
In order not to multiply the solutions, I take the ordinary chloride of gold, used for fixing the impressions, and which is composed of 15 grains of chloride of gold, and 50 grains of hyposulphite of soda, to a quart of distilled water. With respect to chloride of platinum, 4 grains must be dissolved in 3 quarts of distilled water; these two solutions are mixed in equal quantities.
For the sake of brevity in the following description, I will abridge the name of each substance. Thus, I will say, to designate the aqueous solution of bichloride of mercury, sublimate; for the solution of cyanide of mercury, cyanide; for the acidulated oil of petroleum, oil; for the solution of chloride of gold and platinum, gold and platinum; and for the oxide of iron, rouge only.
"The plate is first polished with sublimate and tripoli, and afterwards with rouge, until a beautiful black is arrived at. Then, the plate is laid on the horizontal plate, and the solution of cyanide is poured on it and heated over a lamp, as in fixing an impression with chloride of gold. The mercury is deposited, and forms a whitish layer. The plate is allowed to cool a little, and, after having poured off the liquid, it is dried by rubbing with cotton and sprinkling with rouge.
" It is now necessary to polish the whitish layer deposited by the mercury. With a piece of cotton steeped in oil and rouge this layer is rubbed until it becomes of a fine black. In the last place, it may be rubbed very strongly, but with cotton alone, in order to render the acidulated layer as thin as possible. The plate is afterwards placed on the horizontal plane, and the solution of gold and platinum is poured on. It is heated in the ordinary manner; it is then allowed to cool, the liquid is poured off, and it is dried by gentle friction with cotton and rouge. this operation must be performed with care, especially when the impression is not immediately continued ; for, otherwise, some lines of liquid would be left on the plate, which it is difficult to get rid of. After this last friction the plates should be only acidulated oil is to reduce the metals to powder, and to retain this powder on the surface of the plate, at the same time giving greater thickness to the layer by its unctuous properties ; for the naphtha which results from the distillation of this oil does not produce the same effect, because, being too fluid, it carries away the powder of the metals. It is for the same reason that I have lately recommended the employment of essence of lavender rather than that of essence of turpentine dried, and not polished. This includes the first preparation of the plate, which may be made a long time previously.
I do not think it fit to allow a longer interval than twelve hours to intervene between this operation and iodizing the plate. We left the plate with a deposit of gold and platinum. In order to polish this metallic layer, the plate is rubbed with a piece of cotton, and oil and rouge, until it again becomes black; and then with alcohol and cotton only, in order to remove this layer of rouge as much as possible. The plate is again rubbed very strongly, and passing several times over the same places, with cotton impregnated with cyanide. As this layer dries very promptly, it might leave on the plate traces of inequality; in order to avoid this, the cyanide must be again passed over it, and, while the plate is still moist, we quickly rub over the whole surface of the plate with cotton imbibed with a little oil, thus mixing these two substances; then, with a piece of dry cotton, we rub, in order to unite, and, at the same, to dry the plate, taking care to remove from the cotton the parts which are moistened with cyanide and oil. Finally, as the cotton still leaves traces, the plate is likewise sprinkled with a little rouge, which is removed by gently rubbing.
"Afterwards the plate is again rubbed with cotton impregnated with oil, only in such a manner as to make the burnish of the metal return; it is then sprinkled with rouge, and then very gently rubbed round, to remove all the rouge, which carries with it the superabundance of the acidulated layer.* Finally, it is strongly rubbed with a rather firm pledget of cotton, in order to give the last polish, +
" It is not necessary often to renew the pledgets of cotton imbibed with oil and rouge; they must only be kept free from dust.
The colour of the impression depends on the tint given to the metallic iodide; it may, therefore, be varied at will. However, I have found the violet rose colour most suitable.
" For transmitting the iodine to the plate, the sheet of cardboard may be replaced by an earthenware plate deprived of enamel. The iodine transmitted by this means is not decomposed. It is useless, I may even say injurious, to heat the plate before exposing it to the vapour of iodine.
* This must be done as gently as possible; for otherwise the rouge would adhere to the plate, and would form a general film.
+ In operating on a plate a long time after it has received the first preparation, it is necessary, before employing the acidulated oil and red oxide, to manipulate, as I indicate further on, for the plate which has received a fixed impression. This precaution is necessary for destroying the stains which time may have developed.
In order to remove the sensitive layer, the solution of hyposulphite of soda must not be too strong, because it destroys the sharpness of the impression. 60 grammes of the hyposulphite are sufficient for 1 quart of distilled water".
The elaborate nature of this process is a barrier against its use, since the results are rarely equal to those obtained by the ordinary Daguerreotype, as it is now practised, and the labour to be expended on the preparation infinitely greater.
The advantages which have been derived from the employment of compounds of iodine and bromine, or chlorine, by which the sensibility of the Daguerreotype has been greatly improved, are so great, that, with the incidental notice that we owe the application of bromine to Mr. Goddard, the consideration of them are postponed to the Third Part, as more entirely belonging to the manipulatory details.