Photography

Photography fixes the image formed by a lens on a surface that light changes chemically. Nicéphore Niépce made the oldest surviving camera photograph in 1826 or 1827, and the daguerreotype, made public in Paris in 1839, was the first process sold to the public, with cameras and plates on sale within weeks.

What it is

Photography records an image made of light. A lens throws a small picture of the scene onto a surface coated with a substance that light alters; after treatment, the light and dark parts of the scene stay fixed on that surface for good. The word means “drawing with light”, and the first workers spoke of pictures that drew themselves.

The camera on the plate is the one Alphonse Giroux began selling in Paris in 1839 to the design of Louis Daguerre, the first camera made in quantity for the public. It is two wooden boxes, one sliding inside the other. The front box carries a single lens in a brass barrel, with a round brass cover that swings aside to start the exposure. At the back, a sheet of ground glass shows the image for focusing; it is then replaced by a holder carrying the sensitive plate.

How it works

Artists used portable camera obscuras like this long before photography; a mirror throws the image up onto a glass where it can be traced.

Light from each point of the scene passes through the lens and is brought to a point on the back of the camera. The result is a small, sharp, upside-down copy of the scene, the same image a camera obscura had shown since the Renaissance. Moving the rear box in or out until that image looks sharp on the ground glass sets the focus.

Photography needed a way to keep that image. Some compounds of silver darken in light, and some resins harden in it. Niépce coated a pewter plate with bitumen of Judea dissolved in oil of lavender. Where light struck, the bitumen hardened; afterwards a solvent washed away the soft, unexposed parts, leaving a picture made of bitumen on bare metal.

The daguerreotype used silver. A copper plate coated with polished silver was made sensitive over iodine vapour, exposed for several minutes in the camera, developed over heated mercury, which settled on the parts that light had touched, and fixed in salt water or “hypo”. The result was a mirror-like positive, unique, with fine detail. Talbot’s calotype worked differently: it made a paper negative, from which any number of positive prints could be made by contact, the principle of most of the photography on film that followed.

How to build it

Two simple projects show the two halves of photography at home: a pinhole camera forms the image, and cyanotype paper records light chemically. Do not attempt a daguerreotype outside a professional facility with chemical fume extraction and trained supervision: it uses heated mercury and iodine, both toxic.

Make the camera. Take a light-tight box, such as a shoebox, and paint the inside matt black. Cut a hole about 2 cm across in the centre of one end and tape over it a piece of thin aluminium foil pierced with a needle; a hole of about 0.3 mm suits a box 10 to 15 cm deep. Cover the pinhole with a flap of black card that you can lift and lower: this is the shutter.

Watch the image. Cut a window in the opposite end and tape tracing paper over it. In a bright scene, with a dark cloth over your head and the box, you will see the upside-down image on the paper, exactly as in a camera obscura.

Make a cyanotype. Ready-coated “sun print” paper, used as its maker instructs, is the simplest choice. Cyanotype, published by John Herschel in 1842, uses iron salts that turn Prussian blue in ultraviolet light. Lay a leaf or a fern on the paper in sunshine under a sheet of glass for a few minutes, then rinse the paper in water and let it dry.

A cyanotype photogram: where the fern blocked the light, the paper stayed white.

Going further. Cyanotype is far too slow to take a picture through a pinhole: the exposure would run to weeks. To photograph with the box itself, replace the tracing paper with a light-tight back, seal the edges with black tape, and load black-and-white photographic paper or film in a darkroom. It is then developed and fixed with ordinary darkroom chemicals, used with gloves and good ventilation as their labels instruct.

Safety. Cyanotype chemicals and darkroom solutions irritate skin, eyes and lungs: wear gloves and eye protection, keep them away from food, children and pets, and dispose of them as the labels instruct. If you mix your own cyanotype solution, never heat potassium ferricyanide or mix it with acids. Do not look at the Sun through the pinhole or anything else. Historical processes that use mercury, cyanide or ether belong only in a professional laboratory with fume extraction.

History and evolution

The camera obscura was known long before photography, and by the eighteenth century artists carried portable boxes to trace landscapes. Chemists knew that silver salts darken in light, but nobody could stop the darkening. At his estate at Saint-Loup-de-Varennes in Burgundy, Nicéphore Niépce obtained fleeting camera pictures in 1816 and, in 1826 or 1827, the view from his workroom window that is now the oldest surviving camera photograph, kept at the Harry Ransom Center in Austin. Its exposure is usually given as several days, though some accounts say about eight hours.

A daguerreotype was a single silvered plate, kept under glass in a small hinged case.

Niépce went into partnership with Louis Daguerre in 1829 and died in 1833. Daguerre carried on, and on 19 August 1839 his process was explained in detail to a joint meeting of the Académie des sciences and the Académie des beaux-arts; the French state had bought it and made it free for all to use, except in England and Wales, where a patent was taken out on it. In England Henry Talbot had been making images on paper for several years and announced his first process the same year; in 1840 he devised the calotype negative and made it public in 1841.

From 1851 the wet collodion process of Frederick Scott Archer put negatives on glass, sharper than paper and far quicker than the daguerreotype, but the plates had to be coated, exposed and developed within minutes. By the 1880s factories sold dry plates ready to use: George Eastman began making them for sale in 1880, and in 1888 he sold the first Kodak, a box loaded with film for a hundred pictures, sent back whole to the factory for developing. Colour film spread in the twentieth century, and at its end electronic sensors began to replace the chemistry; in front of them, a lens still forms the image as it did in Giroux’s box.