Emulsion Layers that play with colors in film
Many of us have wondered through the 80′s and 90′s that what is inside a film that takes a color picture. So for you who is still wondering about it; it’s all a chemical reaction. Its simply done to explain it here.
First of all a film can be divided into three parts the emulsion, base and anti-halation backing as seen in the picture below. Emulsion is the part of the film which is sensitive to light because of the silver halide crystals suspended in a gelatin substance. The emulsion may be light brown (in color film) or light gray (in black & white film).
So how do we get color pictures out of these emulsion?
Its simple when these silver halides exposes to light it causes a chemical change in the silver halide crystals and forms an image which is not yet visible to human eyes. When this image is developed and processed through various chemicals in the laboratory it creates a visible image.
The emulsion can further divided into different layers as shown in the picture below.
The emulsion contains color dyes so it can capture all of the colors in a picture. These layers include filters and separates each layer that are sensitive to one of the three primary colors.
How does it recognizes a color?
So how does these chemicals recognizes color. It can be simply explained by the visible spectrum of light. As we all would have studied in our primary classes that every color has different wavelength so in the emulsion base we have yellow, magenta and cyan dye. Here’s the wavelength of these colors:
Yellow light has a wavelength between 590-570 nm
Magenta has a wavelength between 530-500 nm
Cyan lighth has a wavelength between 520-490 nm.
As you can see the wavelength from 590 to 490 is decreasing, the filter in between these emulsion helps them to identify the color. Then you gets a color picture.
Base is the flexible, transparent support for the emulsion. In the early days the base was made of cellulose nitrate which was highly flammable and later in the 1923 Kodak first introduced 16mm films with cellulose acetate base.
Anti-halation backing is a dark coating which is applied to the back of the base so that it does not cause a flare or flash in the image or a double exposure by bouncing back.