By Sherri Conn Rukes
Today, most people take pictures with their phones. However, long ago, we used film. This meant that if you wanted to take a good photo, you had to know some chemistry. People had to understand the science behind light鈥� how chemicals could be used to make the photograph visible.
So, how does using film work? First, a bunch of photons, little bundles of light, have to enter the camera. Then they hit a special piece of plastic with an emulsion on it. An emulsion is a mixture of two or more liquids that normally do not like to mix, like oil and vinegar. But, if we add an ingredient, they can stay together.
The emulsion on a piece of plastic film is a little like muddy water, where tiny particles are 鈥渟uspended鈥� in the water. In this case, the two elements with charges are suspended, silver and bromide. These tiny particles are floating in a kind of gel on the surface of the film.
When a photon hits the tiny particles of , it 鈥渒nocks off鈥� an electron and makes the bromide neutral. That free electron keeps moving around until it can find a silver is missing an electron. As more light hits the emulsion, this . been 鈥渆xposed鈥� and it鈥檚 ready to be 鈥渄eveloped.鈥澛�
When film is developed, chemicals are used to make certain particles on the emulsion to 鈥済ive鈥� their electrons to nearby silver . This forms silver metal, but it doesn鈥檛 look shiny or mirror-like, like fancy silver objects. is thick in some places and thin in others, with lighter and darker spots. image on the film. This means that everything that鈥檚 bright in real life looks dark on the film, and everything that is dark looks bright.
To develop these negatives, a person lays each negative on top of another piece of photographic paper and then shines a light on it. This creates the positive image that reverses the lights and darks. The result is what we think of as a regular photo.
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Sherri Conn Rukes is a chemistry teacher at Libertyville High School.
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