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Only Negative Material: They cannot, therefore, conduct an electric current. If, however, one of the silicon atoms in the structure is replaced by an atom with five outer electrons—such as phosphorus— only negative material four of the phosphorus electrons can link up with the silicon atoms; the fifth electron becomes free to move, and this motion produces a flow of current. Silicon containing an impurity that has an "excess" electron is called n-type (negative-type) material to indicate the availability of electrons, which carry a negative charge.
5. Never be too proud to reshoot a poor negative. Did you make an error in exposure? Did your tripod slip and cause a fuzzy negative? Or did you make one of the other dozens of errors which can almost but not quite ruin a negative? If so, do not try to cover up by struggling with the negative by means of darkroom trickery, but instead shoot the picture over again if that is at all possible. To reshoot is to confess a measure of failure to "your client, of course, but you can make up for that by going all-out for a masterpiece on your second try.
To take these small portraits, Disderi first made a wet-plate negative with a special Camera that had four lenses and a plateholder that could be slid from side to side. Four exposures were made on each half of the plate; thus eight poses could be taken on one negative. A single print from this negative could then be cut up into eight separate portraits. Unskilled labor was used for this work; the production of the cameraman and printer was thus increased eightfold. |
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