PHOTOCHEMISTRY PRIMER BY TIM LAYTON
Photochemistry is the branch of chemistry concerned with the chemical effects of light. It is hard to imagine in the 21st century that photography has anything to do with chemistry. We know the invention of photography was delayed until chemistry made it possible, but not many photographers today associate this information with their current methods.
Generally, photochemistry is used to describe a chemical reaction caused by absorption of ultraviolet (wavelength from 100 to 400 nm), visible light (400–750 nm) or infrared radiation (750–2500 nm).
My personal interest in photochemistry is mainly associated with mixing darkroom processing solutions to process my chemical-based wet prints and modifying film and paper developers to manage issues as they arise in the darkroom.
I also have a keen interest in photochemistry as a means to have direct control over my creative vision. By having the knowledge and experience to control contrast and tonal values within my negatives and prints, I believe that I can better express my vision and message.
As early as 1777 Carl Wilhelm Scheele (1742-1786) made the first scientific study of the effect of light on silver chloride. Scheele had a short life by modern terms, but I find it incredible how much he discovered and contributed to the world in only 44 years of life.
A half century earlier Johann Henrich Schulze used stencils to make light impressions on a mixture of silver nitrate and chalk. Then, the infamous camera obscura - a small darkened box with a lens that cast an image on a ground glass - was used as an artist's aid during the seventeenth and eighteenth centuries. We were building towards a light-sensitive medium and the view camera (wooden box with a bellows and a lens) in order to ultimately create what we know refer to as photographs.
Thomas Wedgewood and Humphrey Davy studied light sensitivity of silver nitrate in the early nineteenth century. They were not successful in making an image that was permanent. During this period there were many claims by chemists of being able to record "camera images" with silver-sensitized paper. We now know they were unable to fix the light impressions and make the images permanent. It must have been a great mystery and tremendous struggle for these people.
Until the chemistry of "fixing" could be figured out, photography would not be fully realized. We now know that we needed to also understand the atomic basics of photography which included the amplifying action of certain chemical compounds.
Louis Jacques Mande Daguerre (1787-1851) and William Henry Fox Talbot (1800-1877) had pieced much of the puzzle together in the late 1830's and into the early 1840's, but struggled with the amplification of compounds earlier mentioned.
Coming full circle nearly two centuries later as I write this text, we fully understand that photography was made possible because of the chemical amplification and chemical fixation of an invisible light impression. The silver photographic image is revealed to be granular particles that blend to ultimately create the tones of a photographic image.
We have evolved to a place where I have to use a qualifier when I am discussing silver-based photography. If I simply used the term "photography", the majority of people would assume a digital camera is being used. I use the term "analog photography" to distinguish the chemical-based photography processes from the contemporary digital application of photography.
Analog photography is effectively composed of three elementary particles: electrons, protons, and neutrons. These three particles are the building blocks of ordinary matter.
As it relates to analog photography, light is composed of particlelike photons, but they are without mass. Over 200 types of elementary particles have been discovered by scientists and chemists, most of them by using high-tech gear that is beyond the grasp of the average person. As it relates to photography, all that matters are the electron, proton, and neutron.
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