DAGUERREOTYPE 



favourable light, to produce the desired effect. Numerous modifications were speedily 

 introduced, and many of them were patented. 



The progressive advance of this branch of the photographic art, though of great 

 interest, cannot be dwelt on in this place. Those who are interested in the inquiry 

 will find the information fully detailed in Hunt's 'Manual of Photography,' last edition, 

 and more recent works. It will be sufficient here to name the more important improve- 

 ments which have become generally adopted. The first advance of real importance was 

 made by Mr. Towson, of Dovonport, who has since that time distinguished himself 

 by the introduction of his system of Groat Circle Sailing. Mr. Towson suggested the 

 use of enlarged lenses ; and by acting with such Dr. Draper, of New York, was the 

 first to procure a portrait from the life. Still this was a tedious process ; but in 1840, 

 Mr. Goddard proposed the use of bromide of iodine, by which infinitely increased 

 sensibility was obtained. From that time the Daguerreotype was generally employed 

 for portraiture, until the facilities of the Collodion process drove it from the field. 



The improved manipulation now resolves itself into : 



Carefully polishing the silver plate after some of the methods previously described, 

 and the application finally of the highest polish by the use of a buffer, the best form 

 being that employed by M. Claudet. 



In a box on a roller, to which there is a handle, fig. 596, is placed a long piece of 

 drab-coloured velvet, which can be drawn out and extended, by means of a second 



596 



537' 



roller, upon a perfectly flat table. The first foot or two, for example, is drawn out ; 

 the plate which has already received its preliminary polishing is placed face down- 

 wards, and being pressed close with the fingers, a rapid circular motion is given to it, 

 and in a few minutes it receives its highest lustre. As the velvet becomes blackened 

 by use, it is rolled off, the portion remaining in the box being always perfectly clean 

 and ready for use. 



The iodising process follows : and for this purpose a box similar to that represented 

 will be found to be very convenient (fig. 597). This iodising apparatus consists of a 

 square box, with a closely-fitting square cover G: 

 false sides are placed at an angle with this box ; 

 a cup D at the bottom contains the iodine, which is 

 covered with a thin gauze screen J j. c is a cover 

 which confines the iodine when it is not required 

 for the plate; this dividing the box into two 

 parts, H H and K K, the former being always 

 full of iodine vapour. When it is desired to 

 iodise a plate, the cover c is removed, the silver 

 plate is placed at E, and the cover G closed. 



The plate is thus placed in the iodine box 

 until it acquires a fine straw-yellow olour. In 

 another box is placed either bromine or some of 

 the many accelerating fluids. If bromine, or any 

 bromide is employed, the plate should remain 

 until it is of a rose colour. As a general rule, 

 if the yellow colour produced by iodine be pale, 

 the red should bo pale also ; if deep, the red 

 must incline to violet. The proper time for ex- 

 posing a plate to any of those chemical substances which are destined to produce the 

 sensitive film must vary with the temperature, and it can only be determined by 

 experience. The sensitive plate is now removed to the camera obscura, for a descrip- 

 tion of which see PHOTOGRAPHY. It is scarcely necessary to say, that the plate 

 must be preserved in perfect darkness until exposed to the image in the camera. 



A few seconds when the plate is properly prepared will be found amply sufficient to 

 produce the best effect. 



The impression must be developed in the mercury box (fig. 598) in the manner 



