Ronny Nanthrup, age 12, of Vashon Island, Wash., for his questions
How are prints developed from a negative?
A film developed from a camera is called 0. negative because it gives an opposite picture of the scenery. A light sky shows up as black, a dark building shows up as light. A print from the negative turns the dark and light areas around and we get a true picture of the scenery. To understand how we get a print from the negative, we must first understand haw the negative gets onto the film.
The film is a tough roll of plastic coated with gelatin. The gelatin is a bags to hold particles of silver bromide, a chemical. The molecules of this chemical are made of silver and bromide and they are very, very sensitive to light. There are millions of these molecules on every square inch of film and, when any one of them is struck by a pinpoint of light, it splits apart into simple atoms of bromide and silver.
The camera lens lets in light carrying an image of the scenery. Strong points of light come from light, bright objects. Weak paints of light come from dark or shady objects. The strong points of light break apart a lot of molecules into atoms of silver and bromide. The weak points of light from dark objects break up only a few.
The film is carefully removed and developed. No extra light is allowed to reach it while it goes through a number of chemical processes. It is given a chemical bath which fixes the silver atoms on the film, Another bath removes the unsplit molecules of silver bromide from the film. The areas where the silver atoms are fixed onto the film show up as dark patches, They are the areas where pinpoints of light from light objects came into the camera.
The print from the negative is made very much like a stencil. The negative is placed on special paper which has been treated which chemicals and coated with our old friend silver bromide.
The two are clamped together and placed under a strong light. The light is stronger through the light patches on the negative and ~ weaker through the dark patches.
The silver bromide, of course, breaks apart more readily where strong pinpoints of light comp through the light areas of the negative. When the picture is clear, the print is developed. The picture is now right side around with light and dark areas corresponding to the scenery.
As with the negative, the developing of the print is a series of chemical baths. One bath firmly fixes the silver Moms to the print, another bath washes away the silver bromide atoms which did not split apart. A bath in clear water washes the print clean, after which it is left to dry.
If the print were not properly developed, it would not last very long. The single silver atoms would not be firmly fixed to the paper, and molecules of silver bromide would continua to break apart until the picture became a blurry dark piece of paper.