DAGUERREOTYPE. The art of im pressing distinct and permanent images on polished metallic surfaces. It received its name from M. Daguerre, who disco vered the mode in 1839, and from whom the French government bought the right to the discovery by giving him an annu ity of 10,000 francs. Compared with the present processes his views were very meagre and incomplete. The views taken were of landscapes, and the process in his hands consisted in coating the silver plate with iodine to a gold color, expos ing in the camera for ten minutes in full sunlight, then exposing the plate to the fumes of mercury, and washing in hypo sulphate of soda. Dr. Draper (now of New York) made the plate more sensi tive by exposing it to chlorine gas after it had received the iodine coating. Views could thus be taken in shade, and in a shorter time ; the impression also was more distinct. Chloride of iodine was soon after substituted for chlorine and io dine separately ; and, still later, bromide of iodine was tried with much greater success.
At the present time the art is practised with wonderful delicacy of manipulation, and perfection in result, in this country. It is acknowledged that American da guerreotypes excel European in beauty of finish, with mellowness and depth of tint. Those taken in France are much better than English ones, which is no doubt due to the clearer and less cloudy skies of France. Perhaps it may be the same reason which causes to be produced better portraits in America than in west ern Europe.
The plate which receives the image is copper coated with silver, either by the ordinary process of plating, or by the electrotype method : the latter is prefer able. The first step in the process is the cleansing the plate. Too much att. ration cannot be devoted to this, as upon it de pends subsequent success. It is impos sible to take a picture on a dirty plate. The slightest trace of oxide, snlphuret, or even film of air adhering to the plate, is sufficient to prevent the appearance of an image. Various plans of cleaning plates are practised. Some use rotten stone and water, made acid by nitric acid ; others use alcohol and ammonia water. These are rubbed on to the plate with small pieces of Canton flannel. The rotten stone should be very fine, and the acid very dilute, else the plate will be streaked. It should be cleaned in the centre first, and that. the edges wiped off. The acid may be removed from the by washing with alcohol, or weak solution of potass ; washing with a solu tion of hydriodate of potass increases the sensitiveness. After being cleaned the plates are buffed, or rubbed with a pad covered with cotton, velvet, or buckskin leather. Great delicacy is employed in the application of the buff, which should remove all traces of the materials used for polishing, and give the final purity to the plate. The plate is now ready to re ceive the coating, or films of iodine and bromine. Small boxes hold the ingre dients in a glass saucer at the bottom, and the plates are placed on the sliding frame above, and passed over the surface of the saucers until they receive the due of these ingredients. This quan
tity varies with the nature of the light and desired appearance of the picture. The depth of the coating is known by the co lor of the plate, which is first straw yel low, then orange, then rose color, violet, steel blue, indigo, and green. If the coating be continued beyond this, it into nto yellow again, and through the same range of colors. The iodine in the box should be quite dry, as the slightest damp on the plate mars the coating. The bromine is used as bromide of lime, made by mixing bromine with fresh slaked lime, till the whole is of an orange tint. As a rule, a good picture will be produced by coating with iodine to a dark orange yellow, then with the bro mide of lime coat to a deep rose red, coat again with iodine one tenth as long as at first coating. The plate now coated is very sensitive, the least exposure to light decomposing its surface. Hence it is ne cessary to shut the plate up in the tablet immediately: this is a close case with a a sliding lid. It is introduced into the camera, and the lid raised when we wish it to receive an image. The selection of a good camera is a sine qua non with the daguerreotype artist. Generally those of Voigtlander of Germany have the best lenses, and are to be preferred. Daguer reotypists, however, in this country pre fer the American cameras. For taking views, the camera invented by Mr. Har rison is by far the best yet made for such purposes. It has been found advanta geous to blacken the inside of the came ra, which absorbs the rays falling on the sides, and thus prevents their reflection and interference with the rays falling upon the plate. A room lighted from above is more suitable than a window or side light, the latter producing the sha dows too deeply marked. A northern aspect is preferred, as the light is more uniform through the day, although light from the south has agreater chemi cal influence. The sitter should not be placed too near the window, nor in front of it. The time of exposure in the came ra varies with the ' light, amount of coat ing, and time of the clay, from 10 se concls to 11 minutes. The operator's judgment is the best guide. The plate is now removed from the camera in the closed tablet, and has to be exposed to the vapor of mercury, in order to bring out the image, for as yet no trace of any delineation Is visible. The mercury bath is an iron vessel of an inverted conical form, the mercury occupying the lower part ; is heated with a spirit lamp until it reaches the temperature of 90 centigrade, when the plate is now placed on the frame attached to the upper part of the bath, where it receives the vapor of the quicksilver. A little window at the side allows the operator to observe the advancement of the process. The image gradually is developed as the mer curial vapor coats the plate, and when the greatest distinctness is produced (which is generally after two minutes), the plate is removed. As far as the image is concerned, nothing more is ne cessary to be done.