CURIOSITY AND THE THRILL OF discovery motivate the amateur scientist to try to understand and perhaps control nature. But unlike the professional, the amateur must conduct research with few supplies and modest equipment. The technique I invented for painting without pigments began as an amateur project more than 10 years ago.

Those readers who have developed their own photographs have probably, noticed that black-and-white prints are sometimes discolored with browns and yellows. I became interested in figuring out what produced those colors, in particular because I knew that the chemicals used in the darkroom would not serve as pigments.

After several years of part-time experimentation, I invented a technique for painting a rainbow of colors on black-and-white photographic papers by applying colorless chemicals. The method utilizes commonly available photographic supplies, and I am delighted to share my methods with the readers of SCIENTIFIC AMERICAN.

My colleague Bryant W. Rossiter of the Eastman Kodak Research Laboratories coined the term "chromoskedasic" to describe my technique. The term "chromoskedasic" means color by light scattering, and my technique exploits this phenomenon. Black-and-white photographic papers contain silver salts that form tiny particles when exposed to light and chemicals. Silver particles that are roughly the same size will scatter certain wavelengths of light and absorb others, producing a specific color. In chromoskedasic painting, the size of the particle is the variable through which color is controlled [see "Chromoskedasic Painting," by Dominic Man-Kit Lam and Bryant W. Rossiter; page 80].

Chromoskedasic techniques require no special skills, although a degree of artistic talent will obviously enhance the results. An eye for art also helps in deciding which images are worth keeping and which are best left in the darkroom.

I highly recommend that readers assemble all necessary materials and dilute all needed solutions before removing the photographic paper from its protective box. For the paintings described below, I used Kodak papers and photographic solutions. Other brands of materials should work just as well.

Readers should heed the warnings on the various chemicals. (You can obtain additional hazard information, free of charge, from a photographic chemical supplier by requesting "Material Safety Data Sheets" for specific products.) When mixing photographic chemicals, wear safety glasses and old clothes that cover you completely. Some of the chemicals are strong acids that can be very harmful if ingested or splashed on the skin or eye. Never pour water into a concentrated acid. Dilution should always be performed by carefully adding the acid to the water. All the chemicals mentioned in this article should be diluted to the desired concentration with water.

Over the years, I have made hundreds of paintings and have taught the technique to my daughter and to friends. In the following paragraphs, I describe three projects in order of increasing sophistication. I suggest that readers first adhere to my instructions and, before moving on to the next project, experiment a bit to get a feel for the process.

I used only the most basic chromoskedasic methods to create Among the Coral Reefs, the abstract painting at the right. I removed a piece of Kodak Polycontrast 3RCF black-and-white photographic paper (60 by 40 centimeters) from its protective covering. After exposing the paper to dim red light for five minutes, I poured about half a cup of a 10 percent solution of Kodak Ektamatic S30 Stabilizer onto the paper. I swirled the stabilizer on the paper in an attractive pattern. The regions exposed to the stabilizer would eventually emerge as light yellow.

On other areas of the paper, I immediately poured a small amount of 10 percent solution of Kodak S2 Activator, followed by a 50 percent solution 5 of Dektol. These chemicals produced reds, oranges, yellows, greens, blues and grays. I exposed the paper to light from a fluorescent lamp for five minutes. Finally, I bathed the paper in a 50 percent solution of Kodak Rapid Fixer, then rinsed the paper with water and allowed it to dry.

With a little more effort, readers should be able to create images like To Run, shown at the right below. Using an artist's brush and black ink, I painted a running horse on rice paper. I then took a photograph of the horse using Kodak black-and-white film and developed the negative. I used a photograph enlarger to transfer the negative image onto a piece of Kodachrome paper (20 by 25 centimeters).

Immediately after, under red light, I poured a 10 percent solution of stabilizer onto the paper and swirled it around. I did the same with a 10 percent solution of S2 Activator on the same part of the paper; the stabilizer and activator combined to make oranges. To produce a deep red-orange color, I applied a 50 percent solution of Dektol. Using a rag, I spread a 50 percent solution of fixer over the entire paper and then submerged the paper in the fixer for 20 minutes. Finally, I washed the paper in a water bath for 30 minutes and let it dry.

To create Autumn in New England, the impressionist painting shown at the top, I used both chromoskedasic techniques and ordinary enamel paints. Under red light, I cut a 100-by300-cendmeter piece of black-and-white, polycontrast photographic paper from a large roll. Using a brush dipped in full-strength S30 Stabilizer, I drew the peak of a snow-covered mountain. I then turned on the fluorescent room lights, exposing the paper for five minutes.

To add ivory-colored details on the mountain, I brushed on, under red light, a 20 percent solution of stabilizer. I painted other areas with the diluted stabilizer to make the outline of a lake. To produce brown tones, I worked these areas over with a 50 percent solution of S2 Activator. After dipping a fountain pen in the activator, I outlined trees in the foreground of the picture. I shaded the trunks brown by applying stabilizer and then activator.

I exposed the material to fluorescent light for a total of about 30 minutes and then applied a 50 percent solution of fixer with a spray bottle over the entire piece of photographic paper. After 20 minutes, I washed the entire paper with a garden hose and allowed it to air-dry. I then used enamel paints to add white mist on the mountains, blue water in the lake and yellow and red leaves on the trees.

I am sure readers will find many interesting effects by experimenting with such chromoskedasic techniques. I can not even begin to imagine the various works of art that might be created using this medium. Will the new medium provide a palette for the creative mind of a new da Vinci or Picasso?

Bibliography

NEBLETTE'S HANDBOOK OF PHOTOGRAPHY AND REPROGRAPHY: MATERIALS, PROCESSES AND SYSTEMS. C. B. Neblette. Van Nostrand Reinhold, 1977.

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