A Manual Of Photography

IMPROVEMENTS IN DAGUERREOTYPE. 45 “ It is by superposing on the plate several metals, reducing them to powder by friction, and by acidulating the empty spaces which the molecules leave, that 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 com- posed 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 trans- parency 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 pre- cisely, and since immediately beyond it the bromine attacks the silver, and is opposed to the formation of the image.1 11 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 op- posed to the formation of what is called the veil of bromine. This facility must not, however, be abused ; for the layer of gold, being very thin, might be attacked, especially if too much polished? The process which I am about to give may, perhaps, he 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 em- ployed, 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 1 Every one knows that the dry vapour of bromine is more favourable than that which is obtained by means of a solution of bromine in water; lor the latter has the inconvenience of carrying with it moisture which con- denses on the surface of the plate. The employment of the oil, which I indicate further on, neutralises this effect, and gives to the vapour of bromine diluted with water the same property as that of dry bromine.—These notes öre Daguerre's. 2This is so true, that if an impression be made on a plate which has been fixed several times, it may be exposed to the vapour of bromine as many times more than the necessary time it lias received layers of gold.