silver, and the stronger the light, the more complete the separation. If the image the light draws on the film shows two men, one wearing a white garment and the other a black garment, it is self-evident that the light reflected from the white garment will bring about, in the spot of the film on which it falls, a separation of bromine and silver far greater than the separation brought about by the scant light reflected from the black garment.
Developing the Image
Now that the light has recorded the image on the film, the next operation is developing the film (Development). For this purpose the film is placed in a chemical solution containing organic compounds that increase the separation of the silver from the bromine in those spots of the film that were exposed to light; the bromine dissolves in the water, leaving behind black grains of silver.
As for the places that were not exposed to strong light, they still retain some silver bromide, which must be removed before the film is exposed to light. For this purpose the film is placed in a solution containing hyposulfate of soda (Hyposulfate de Soude), which reacts with the silver bromide to form a soluble substance.
The film, then, now contains black spots in the places where it reacted with strong light, white places where no light reached it, and spots ranging between black and white according to the strength of the light that fell on them. Or, in other words, if we return to the picture of the two men mentioned above, we see that the white garment will appear black and the black garment white. This is what we call the negative image (Negatif). To make it a positive image, the negative film is laid on a piece of glossy paper coated with the same sensitive substances the film contains; there take place on the surface of the glossy paper the same reactions that take place on
the film, except that what was black becomes white and what was white becomes black, because the light does not penetrate to the sensitive paper through the black part of the film (the part which recorded the image of the white garment), while it passes easily through the white part (the part which recorded the image of the black garment).
Color Films
The light-sensitive part of these films is made in the same way as that of ordinary films. The addition here is that the film is coated with a transparent coating containing the colors blue, red, and green, for these are the primary colors — that is to say, we can obtain almost any color we wish if we mix these colors, or some of them, in the right proportions. The film is exposed to light in such a way that the rays reach the sensitive chemical compound
after piercing the three colored layers. If we wish to photograph a red rose, the rays pierce the red color without affecting the blue or the green; and if we wish to photograph a green tree, the green passes through the film without affecting the red or the blue, but acts on the sensitive compound behind the green part of the film. If, however, the color is a compound one — yellow, for example — it passes through both the red and the green. This method thus separates the colors from one another. And when the color film is developed, the grains of silver increase behind the places on which the red light fell, for example, so that this color appears clearly, while the green or the blue does not appear, because the red light does not penetrate through them and so cannot act on the sensitive compound behind them.
PERSONNA
MADE U.S.A.
Precision
Unique of its kind,
like a rare jewel
So said those who have tried "Personna" blades.
So will you say, too, when you try them.