TONI GENTILLI

 The Evidence of Absence (Cyanometer Project), 2013

 “Evidence of absence is not absence of evidence” is something I heard often during my former career as an archaeologist. Though widely interpreted, this idiom generally pertains to how scientific proof is ascertained, its relationship to the positive evidence of existence, and notions of truth. I engage these same topics by investigating photography’s long-standing capacity to both document facts and portray fictions, while challenging the expectation that a photograph is a picture of something  – a discernable visage extracted from reality – by distilling it into its essential nature: a recording of light.

The content, form, and materials of my project are predicated on the cyanometer, a quasi-scientific apparatus invented in the late 18th  century by Swiss mountaineer and professor of natural philosophy Horace-Bénédict de Saussure. Filled with the desire to measure the blueness of the sky, de Saussure created a circular monochromatic scale of cyan using Prussian blue pigment applied to white paper. He simply held the instrument to the sky at varying elevations as a qualitative reference for ascertaining its hue. De Saussure theorized the blueness of the sky was an optical effect that changed in relation to moisture content, but proof of the proposed phenomena could not be attained with his device. Subsequent scientists surmised the perceived blueness of the sky is an effect of light scattering in the atmosphere. Despite its inability to provide precise measurements, the method of recording data relative to a visual standard like de Saussure’s cyanometer is still used today by archaeologists and geologists for describing soils with the Munsell color chart.

Prussian blue, discovered in the early 18th  century, is an artist’s pigment formulated from an iron compound. Nearly 100 years later, one of the principal chemical constituents of Prussian Blue (potassium ferricyanide) provided the basis for a pioneering photographic process called cyanotype. Invented by Sir John Frederick William Herschel in 1842, the cyanotype process uses UV-light to create photographic images on paper sensitized with iron salts. Like de Saussure, Herschel was interested in observing and recording the heavens. Both he and his father, Frederick William Herschel, were renown astronomers whose notable discoveries, along with scientific innovations in optics, chemistry, and photography, forever altered the course of history.

To approximate the gradation of tones in a cyanometer, I devised a two-part photographic process wherein I recorded the quality of light in the sky the day before, and then again for the duration of, six selected solar events that occurred over the course of a year. The events include: Perihelion (January 2, 2013), Vernal Equinox (March 20, 2013), Summer Solstice (June 21, 2013), Aphelion (July 5, 2013), Autumnal Equinox (September 22, 2013), and Winter Solstice (December 21, 2013). I used a Holga camera to make successively more dense photographs ranging between 1 and 12 exposures in each frame on a single roll of black and white film. Every photograph on a given roll of film is of the same portion of the sky, chosen at random. While taking the pictures, I noted my location, the azimuth of the sun, and time of day the film was exposed. I included few geographic features in the pictures themselves with the intention of focusing on recording the physical presence of light via its affect on the chemistry of the film. I carried this intent through to the printing process, which relies upon light-senstive chemistry to expose the images, and also, through its own manifestation, creates visual evidence of the lightinduced reactions inherent to the process. I made each print by placing a roll of film on paper coated with cyanotype and exposing it outside for the duration of sunlight available that day.

I imposed this set of constraints on my process as a proxy for the scientific method. Although adhered to rigorously, the precision of my arbitrary constraints does not substitute for science, even if the photographs are, in fact, physical recordings of actual phenomena. The verity of these photographs is further convoluted by their relationship to time. Rather than fixing a single fleeting instant, each photograph instead layers several discrete moments and embeds them within the expanded chronology of day-long events, that span a period of 12 months.

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