142 ORIGINAL PROCESS 



555. But in the reflected sunshine, the eye cannot support the effulgence of the rays. 

 It is, therefore, absolutely necessary to pass them through some blue medium, which 

 shall abstract from them their heat, and take away their offensive brilliancy. I have 

 used for this purpose blue glass, and also ammoniaco-sulphate of copper, contained in a 

 large trough of plate glass, the interstice being about an inch thick, and the fluid dilu- 

 ted to such a point as to permit the eye to bear the light, and yet to intercept no more 

 than was necessary. It is not requisite, when coloured glass is employed, to make use 

 of a large surface; for if the camera operation be carried on until the proof almost so- 

 larizes, no traces can be seen in the portrait of its edges and boundaries ; but if the pro- 

 cess is stopped at an earlier interval, there will commonly be found a stain correspond- 

 ing to the figure of the glass. 



556. The camera I have used, though much better ones might be constructed, has 

 for its objective two double convex lenses, the united focus of which for parallel rays 

 is only eight inches; they are four inches in diameter in the clear, and are mounted in 

 a barrel, in front of which the aperture is narrowed down to 3j inches, after the man- 

 ner of DAGUERRE'S. 



557. The chair in which the sitter is placed has a staff at its back, terminating in 

 an iron ring, that supports the head, so arranged as to have motion in directions to suit 

 any stature and any attitude. By simply resting the back or side of the head against 

 this ring, it may be kept sufficiently still to allow the minutest marks on the face to be 

 copied. The hands should never rest on the chest, for the motion of respiration dis- 

 turbs them so much as to bring them out of a thick and clumsy appearance, destroying 

 also the representation of the veins on the back, which, if they are held motionless, are 

 copied with surprising beauty. 



558. It has already been stated that certain pictorial advantages attend an arrange- 

 ment in which the light is thrown upon the face at a small angle. This also allows 

 us to get rid entirely of the shadow from the background, or to compose it more grace- 

 fully in the picture; for this, it is well that the chair should*be brought forward from 

 the background from three to six feet. 



559. Those who undertake Daguerreotype portraitures will, of course, arrange the 

 backgrounds of their pictures according to their own tastes. When one that is quite 

 uniform is desired, a blanket or a cloth of a drab colour, properly suspended, will be 

 found to answer very well. Attention must be paid to the tint: white, reflecting too 

 much light, would solarize upon the proof before the face had had time to come out, and 

 owing to its reflecting all the different rays, a blur or irradiation would appear on all 

 edges, due to chromatic aberration. It will be readily understood that if it be desired 

 to introduce a vase, an urn, or other ornament, it must not be arranged against the back- 

 ground, but brought forward until it appears perfectly distinct on the obscured glass of 

 the camera. 



560. Different parts of the dress, for the same reason, require intervals, differing con- 

 siderably, to be fairly copied, the white parts of a costume passing on to solarization be- 

 fore the yellow or black parts have made any decisive representation. We have, there- 

 fore, to make use of temporary expedients. A person dressed in a black coat, and 



