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"So great is the difference in many faces, when inspected in opposite directions, that one of the two views, however accurately taken, would not communicate the likeness-- it not being, the usually observed characteristic form. When the right view of the head is obtained, it is first necessary to consider the size of the plate it is to be taken on, so as to form an idea of the proportion the head should bear to it. The mind must arrange these points before we commence, or we shall find everything, too large or too small for the happy proportion of the picture, and the conveying of a just notion of the stature. The work will have to be done over, and time sacrificed, if this is not attended to. The adjustment of the head to the size of the plate (as seen from the margin of the mat), is not to be taught: everyone must bring himself, by scrutinizing practice, to mathematical accuracy; for something will be discovered in every face which can be surmounted only by experience.
"The eye nearest the camera, in a three-quarter-face, is placed in the middle of the breadth of the plate; the chin, in a person of middle stature, in the middle of the length, and higher according to the proportional height of the person."
In regard to the proper elevation of the camera, it may be here stated that I have found it best in taking portraits where the hands are introduced, to place the camera at about equal height with the eyes of the sitter, in order to bring the face and hands equi-distant from the tube. It will be found, if the above be followed, that by attaching a string to the camera tube, and making a semi-circle, that the face and hands of the sitter will occupy a corresponding distance, and the consequence is that the impression will appear without the hands being magnified. It has been found that a person with a freckly face can have as fine, fair, and clear an impression as the most perfect complexion; this may be done by the subject rubbing the face until it is very red. The effect is to lessen the contrast, by giving the freckles and skin the same color and the photogenic intensity of the red and yellow being nearly the same, an impression can be produced perfectly clear.
When a child is to be taken, and there are doubts of its keeping still, the operation may be accelerated by placing it nearer the window bringing the screen nearer, and placing a white muslin cloth over the head; this will enable you to work in one third of the usual time. Should the person move, or the plate become exposed to the light, it may be restored to its original sensitiveness by placing it over the quick, one or two seconds.
Developing the Daguerreotype.--After the plate has been submittedto the o peration of the light, the image is still invisible. It requires to be exposed to the vapors of heated mercury. It is not absolutely necessary to apply artificial heat to the mercury to develop the image, for fair proofs have been produced by placing a plate over the bath at the ordinary temperature of the atmosphere. This plan, however, requires a long time and cannot be adopted in practice, even if it were advisable. The time more usually required in developing the image over the mercurial vapors, is about two minutes, and the temperature is raised to a point necessary to produce the desired effect in that time. This point varies as indicated by different scales, but for the ordinary scales it is not far from 90 deg. cen.
The mercury bath is accompanied with a centigrade thermometer, by which the heat is regulated. Those furnished by the manufacturers are not always correct, and it requires some experience to find the proper degree on the scale.
I would here remark that it is advisable, when placing the spirit lamp under the bath, to so arrange it that the position of applied heat should always be on the same point, viz., should the heat be directly under the bulb containing the thermometer it would raise the mercury in the tube to the point marked, and the temperature of that in the bath would be far below what it should be; hence it is (where time is followed for developing) that many failures occur. This is observed more readily in the large baths made of thick iron, particularly upon first heating. In practice I apply the heat as nearly as possible between the centre of the bottom of the bath and the bulb containing the mercury tube. It is advisable to keep the lamp lighted under the bath from the time of commencing in the morning to the close of business at night. By this means you have a uniformity of action, that cannot be otherwise obtained.
It is well known to the experienced Daguerreotypist, that different atmospheres have a decided effect upon the mercury in developing the Daguerreotype. It will require a greater degree of heat for one atmosphere than for another. Experience alone determines this little difference.
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