Solargraphy: half a year in a single picture

Solargraphy is photography without a shutter and without a developer. A pinhole camera, usually a can with a sheet of black and white photo paper inside, stays fixed in one place for weeks or months. Over that time the sun burns its daily arcs straight into the paper: the image needs no development, it is already visible when you open the can, and all that remains is to scan it.

What comes out looks like no other photograph. Above the house, the tree, the street that sat still in front of the pinhole for months, there is a fan of bright lines: each line one day, each gap one cloud. Half a year of weather, readable on a single sheet.

The equipment barely deserves the word. An empty can, a scrap of thin metal, a needle, a sheet of photo paper, tape. The rest is a good spot and the willingness not to check on it for half a year.

A picture nobody develops

In ordinary black and white photography the exposed image is invisible. A fraction of a second of light changes the silver in the paper so faintly that only a developer, amplifying that change millions of times, makes a picture appear. Why even a spoonful of instant coffee can do that job is the subject of Caffenol: the developer made from coffee.

Solargraphy takes the opposite road. When light falls on the paper not for a second but for a thousand hours, the change no longer needs amplifying: the silver salt breaks down into metallic silver on its own, and the paper darkens wherever light has been. Photographers of the nineteenth century knew this as printing out. The sun itself, the brightest thing in the frame, burns the clearest trace of all.

Hence the strange ground rule of this process: no developer, no fixer, no darkroom. Any chemical bath would only destroy this finished image. The paper comes out of the can, gets scanned, done.

The camera: a can, a hole, a sheet of paper

An aluminium drinks can is the classic body. A tin with a lid or an old film canister works just as well. The can must be light tight, with enough room inside for the paper to sit curved against the wall.

Build it like this:

1. Cut the top off a drinks can. In the middle of the wall, make an opening of about five millimetres. This is not the pinhole yet, only its mount.
2. The pinhole itself goes into a separate piece of thin metal, for instance a patch cut from a second can. Pierce it with a fine needle, tip only, then smooth the back with fine sandpaper. You are aiming for 0.2 to 0.35 millimetres, round, with no burr. Tape the patch over the opening from the inside.
3. In dim light, place a sheet of black and white photo paper into the can, curved, emulsion facing the hole, the hole itself left clear. Do not crease it.
4. Seal everything: lid on or foil over the top, then black tape along every seam. A last strip of tape goes over the pinhole as a shutter, to be peeled off once the can is mounted.

Whether the hole measures 0.25 or 0.3 millimetres will not decide between success and failure here. An exposure of months forgives almost any imprecision. The hole only must not be too large, or stray light washes the trails out.

Where to put it

The can needs a clear view of the sun's path. In the northern hemisphere that means facing south, or at least southeast or southwest. Some sky has to be in the frame, or there will be no trails. Some foreground should be in the frame, or there will be nothing but trails.

More important than direction is rigidity. The can must not move a millimetre in six months, or the lines smear. Cable ties around a drainpipe, a fence post or a railing have proven themselves: two of them, pulled tight, the pinhole tilted slightly upward. Balcony, garden, window ledge, all fine, as long as no roof overhang blocks the sky.

Two things before you walk away. Ask permission if the spot is not yours, because a taped up can on a stranger's fence will sooner or later be removed by someone who had no idea what it was. And write down the date and the place, ideally on the can itself: a weatherproof note with one line of explanation has saved many cameras.

Solstice to solstice

You can hang a can at any time. After a week the first trails are in the paper, and a month makes a complete picture.

The classic span, though, is the half year between the solstices, June 21st to December 21st or the other way round. The reason is simple: between those two days, the sun's noon height travels once from its lowest point to its highest. The paper then shows the whole fan, the flat arc of the winter solstice at the bottom, the high summer arc at the top, and half a year in between, day by day.

Upward, there is no fixed limit. Solargraphs have been exposed for several years. How far exposure time can be pushed at all is something one of Przemek's works demonstrates: a single exposure at Münchner Freiheit in Munich ran for eight years, from 2006 to 2014.

Reading the trails

A finished solargraph is a weather log, and you can read it like one.

• Each line is one day. The sun crosses the frame once, following its arc.
• The height of the line is the season. High arcs are summer days, flat ones near the bottom edge are winter days.
• Gaps are clouds. The trace forms only in direct sun. An unbroken line was a clear day, a dashed one was changeable, and where a whole arc is missing, the day was grey.
• The foreground is pale and still. Houses, trees and roads receive just enough light in months for a faint image. Everything that moved, people, cars, birds, has vanished. Only what stayed is in the picture.

Take it down, scan it, invert it

The minutes after taking the can down decide the picture, and what they call for above all is speed.

Open the can in the weakest light you can find, never in the sun. What you are holding is a negative in odd colours, brown, grey, sometimes blue and violet, even on black and white paper. That is normal.

Scan the paper at once, in a single pass, at high resolution. The scanner's own light exposes it further, so there is no test run and no second attempt with better settings: the first scan is the scan. Afterwards the paper goes into a light tight envelope. It stays sensitive forever and darkens a little with every light it meets. From now on, the file is the actual picture.

On the computer, invert the negative, mirror it, and pull up the contrast. The brown haze usually turns a deep blue, the sun trails turn into bright lines. It needs no more editing than that.

How solargraphs fail

It pays to know the four most common endings before you start.

• Water. The most frequent one. Rain and condensation creep through every leaky seam, the paper buckles and grows mould. Good tape on every edge helps, and so does a small drain hole at the lowest point of the can. Some water damage ends up looking better than the plan did. You cannot count on that.
• People. Cans get torn down, thrown away, reported. Hang them inconspicuously, out of easy reach, with the explanatory note attached.
• Light. One leaking seam exposes the whole sheet, and months later there is nothing but grey fog. When in doubt, one more layer of tape.
• Movement. A can that works in the wind draws trembling, doubled trails. Two cable ties instead of one.

The best insurance is quantity: hang three cans, and in half a year one of them will almost certainly hold a picture. A single can is more of an experiment.

A different kind of waiting

Przemek has been photographing since 1974, and since 2014 he has worked in heliography, the sun drawing directly onto light sensitive material. Solargraphy is the most approachable form of that fascination: slow light writing itself into a picture, and a person who has to bear not looking for months.

The Both In Time camera is not a solargraphy camera. Its exposures run from four seconds to a few hours, not months, and its waiting is of a different kind: two people share one negative, each exposes one half, and until both are done, nobody sees anything. In solargraphy you wait for the sun; with this camera you wait for a person. The material is the same in both cases: light, paper and time.