Photography

Why This Matters

Photography is the first technology that captures reality with absolute precision. Before photography, all records depended on human memory and artistic skill. A photograph of a wound helps a doctor train others. A photograph of a land survey settles disputes permanently. A photograph of a machine part lets someone in another settlement build an exact copy. Photography is mechanical memory.

Camera Principles

All photography starts with the same physics: light travels in straight lines. If you make a small hole in one wall of a dark box, light from the scene outside enters through the hole and projects an inverted image on the opposite wall.

Building a Pinhole Camera

This is the simplest possible camera and requires zero optics.

Materials: A light-tight wooden box (20 x 20 x 25 cm), thin metal sheet (tin can), needle, black paint, and a light-sensitive plate or paper.

Construction:

1. Paint the entire interior of the box flat black — any reflective surface will fog the image
2. In the center of one end, cut a hole 2 cm in diameter
3. From the tin sheet, cut a small square (3 x 3 cm). Pierce its center with the finest needle you have. The hole should be approximately 0.3-0.5 mm in diameter
4. Mount the tin square over the hole in the box, centering the pinhole
5. On the opposite end of the box, mount a frame to hold your light-sensitive plate or paper
6. Build a simple sliding cap or flap to cover the pinhole (this is your shutter)

Using it:

1. In your darkroom, load a light-sensitive plate into the frame inside the box
2. Take the camera outside, set it on a stable surface aimed at your subject
3. Remove the pinhole cover for the required exposure time (typically 1-30 minutes in bright sunlight)
4. Replace the cover and return to the darkroom to develop

Pinhole Size Matters

Too large: blurry image. Too small: diffraction blurs the image and exposure takes too long. For a box 25 cm deep, aim for a 0.4 mm pinhole. Test by holding the pinhole plate up to bright sky — you should barely see light through it.

Lens Camera

A glass lens gathers far more light than a pinhole, enabling shorter exposures and sharper images.

Basic lens camera design:

1. Use a convex lens (plano-convex or biconvex) from your optics work
2. Mount it in a tube that slides in and out of the camera box for focusing
3. The distance from lens to plate when a distant object is in focus equals the lens’s focal length
4. For closer subjects, extend the lens further from the plate
5. Add a stop (a piece of metal or card with a hole) behind the lens to control aperture

Lens Focal Length	Image Angle	Best For
50-75 mm	Wide	Landscapes, buildings
100-150 mm	Normal	Portraits, general
200-300 mm	Narrow	Distant subjects, details

Light-Sensitive Chemistry

Making Silver Nitrate

Silver nitrate is the foundation chemical. You need metallic silver and nitric acid.

1. Dissolve small pieces of clean silver (coins, jewelry, native silver) in dilute nitric acid (1 part acid to 3 parts water)
2. The silver dissolves with release of brown nitrogen dioxide gas — do this outdoors or under a strong draft
3. When the acid stops reacting, gently heat the solution to evaporate most of the water
4. Cool slowly — silver nitrate crystals form as clear, colorless rods
5. Store in a dark glass container. Silver nitrate stains skin black and is mildly toxic — handle with wooden tongs

Silver Nitrate Safety

Silver nitrate is corrosive and will permanently stain skin, clothing, and wood a deep black color. It is also toxic if ingested. Always use wooden or glass tools, never metal. Wear cloth gloves you can discard. Work in dim light — silver nitrate solutions are light-sensitive even before coating.

Forming Silver Halide

Silver halide crystals (silver chloride or silver bromide) are the actual light-sensitive compounds.

Silver chloride method (simplest):

1. Dissolve silver nitrate in distilled water (10 g per 100 mL)
2. Separately dissolve common salt (sodium chloride) in water (6 g per 100 mL)
3. Slowly pour the salt solution into the silver nitrate solution while stirring
4. A white precipitate (silver chloride) forms immediately
5. This milky suspension is your raw emulsion

Silver bromide method (more sensitive to light):

1. Replace salt with potassium bromide (available from wood ash processing or mineral deposits)
2. Same procedure — silver bromide precipitate forms as a pale yellow suspension
3. Silver bromide is roughly 10 times more sensitive to light than silver chloride, meaning faster exposures

Coating Plates and Paper

For glass plates:

1. Dissolve 4 g of gelatin in 50 mL of warm water (40 degrees C)
2. Add your silver halide suspension and mix thoroughly in dim red light
3. Pour the warm emulsion onto a clean glass plate, tilting to spread evenly
4. Set the plate level and let the gelatin set in complete darkness
5. When firm, the plate is ready to use — store in a light-tight box

For paper:

1. Brush a sizing layer (dilute gelatin or starch) onto smooth, heavy paper
2. Let it dry completely
3. Brush on the silver halide-gelatin emulsion under red safelight
4. Dry in total darkness

Temperature Control

Gelatin sets around 25 degrees C and melts around 35 degrees C. If your emulsion is too hot, it runs off the plate. If too cool, it gels before you finish coating. Work in a room around 20-22 degrees C and keep the emulsion at exactly 35-40 degrees C in a water bath.

Exposure

Aperture

The aperture is the size of the opening that admits light. Smaller aperture means sharper image (greater depth of focus) but longer exposure time.

Make aperture stops from thin metal or card stock with different sized holes. A set of 5 stops is sufficient:

Stop	Hole Diameter	Relative Exposure Time	Use
Largest	25 mm	1x (fastest)	Dim light, moving subjects
Large	18 mm	2x	Overcast day
Medium	12 mm	4x	Bright day, general
Small	8 mm	8x	Maximum sharpness
Smallest	5 mm	16x (slowest)	Maximum depth, still life

Exposure Time

Without a light meter, use these starting points for silver bromide gelatin plates in direct sunlight:

Subject	Aperture	Time
Landscape, bright sun	Medium	2-5 seconds
Building in shade	Large	10-30 seconds
Portrait (outdoor shade)	Largest	5-15 seconds
Interior with window light	Largest	1-5 minutes
Night, by firelight	Largest	10-30 minutes

The emulsion sensitivity varies with how you prepared it. Make test exposures first — expose strips of your coated paper for different durations and compare the results after developing.

Developing and Fixing

The Darkroom

You need a completely light-tight room. Any stray light fogs unexposed plates.

Setup:

1. Choose a room with no windows, or cover windows with multiple layers of dark cloth sealed at edges with clay or putty
2. Seal the door with cloth strips around all edges
3. Wait 15 minutes in the sealed room — if you can see any light at all, find and seal the leak
4. Install a safelight: a dim candle or oil lamp behind two layers of deep red cloth or glass. Silver halide is least sensitive to red light, so dim red illumination lets you see without fogging plates
5. Set up three trays (wood, glass, or glazed ceramic — never metal) in a row: developer, water rinse, fixer

Developing the Image

When a silver halide plate is exposed to light, the crystals that received light undergo a tiny chemical change. They look unchanged to the eye — this is the “latent image.” The developer amplifies this change, converting exposed crystals to visible metallic silver (dark) while leaving unexposed crystals unchanged.

Gallic acid developer (simplest):

1. Dissolve 5 g of gallic acid (from oak galls or tannic acid sources) in 500 mL of water
2. Add 2 g of silver nitrate dissolved in 50 mL of water
3. Immerse the exposed plate in this solution under red safelight
4. Watch the image appear — dark areas develop first (these received the most light)
5. When the image looks complete (2-10 minutes), remove the plate

Pyrogallol developer (better contrast):

1. Dissolve 5 g pyrogallol (made by heating gallic acid) in 500 mL water
2. Add 1 g sodium carbonate (washing soda) dissolved in 50 mL water
3. Same immersion procedure — the image appears in 1-5 minutes

Stop Development

If you leave the plate in developer too long, the unexposed areas begin to develop too, producing a dark, foggy image. Pull the plate as soon as highlights (bright areas in the scene) start to show density. Immediately rinse in clean water for 30 seconds.

Fixing

The developed plate still contains unexposed silver halide, which will darken if exposed to light. Fixing dissolves the remaining silver halide, making the image permanent.

Sodium thiosulfate fixer (hypo):

1. Dissolve 200 g sodium thiosulfate (available from natural mineral deposits — look for clear prismatic crystals near hot springs or volcanic areas, or synthesize from sodium carbonate and sulfur) in 1 liter of water
2. Immerse the developed and rinsed plate in fixer for 5-10 minutes
3. The milky, unexposed areas of the plate gradually clear to transparent (on glass) or white (on paper)
4. When fully cleared, rinse in running water for 20-30 minutes to remove all fixer residue

Fixing Completeness Test

The plate is fixed when no milky areas remain when viewed against a white background. If milky patches persist after 10 minutes, your fixer is exhausted — mix fresh solution.

Printing

The developed plate is a negative — areas that were bright in the scene are dark (dense silver), and areas that were dark in the scene are clear or light. To get a positive image, you print from the negative.

Contact Printing

The simplest method. The print is the same size as the negative.

1. In the darkroom under safelight, place a sheet of silver halide-coated paper emulsion side up
2. Place the negative on top, emulsion (image) side down, in direct contact
3. Press together under a sheet of glass
4. Expose to sunlight or bright lamp light — start with 30 seconds and adjust
5. Develop, rinse, and fix the paper print exactly as you did the negative
6. The result is a positive image — darks are dark, lights are light

Enlarging

To make prints larger than the negative, project the negative image onto paper using a lens.

1. Mount the negative in a frame above the paper
2. Place a lamp above the negative
3. Between the negative and paper, position a lens that focuses the projected image onto the paper surface
4. The distance from negative to paper determines enlargement — further apart means larger
5. Expose, develop, and fix as usual

Photographic Processes Compared

Process	Invented	Sensitivity	Ease	Output
Daguerreotype	1839	Low	Hard	Positive on silver plate, mirror-like
Calotype	1841	Low	Moderate	Paper negative, unlimited prints
Wet collodion	1851	Medium	Hard (time-sensitive)	Glass negative, sharp
Dry gelatin plate	1871	High	Easiest	Glass negative, store for weeks

Recommendation: Start with the dry gelatin plate process described in this article. It is the most forgiving — plates can be prepared days in advance, and exposure times are the shortest.

The Daguerreotype

For historical interest and for making unique, highly detailed images:

1. Polish a silver-plated copper sheet to a mirror finish
2. Fumigate the plate over iodine crystals until it turns gold (forms silver iodide)
3. Expose in camera (1-30 minutes in bright sun)
4. Develop by fuming over heated mercury (EXTREMELY toxic — use outdoors with wind blowing away from you)
5. Fix in sodium thiosulfate
6. The result is a one-of-a-kind mirror image with extraordinary detail

Mercury Danger

Mercury vapor is cumulative and lethal. Mercury-developed daguerreotypes are a historical curiosity, not a practical method. Use gelatin dry plates instead. If you must attempt daguerreotypes, work outdoors, upwind, and limit exposure to mercury fumes.

Practical Applications

Photography is not a luxury. It has immediate, practical value for a rebuilding civilization:

Application	What to Photograph	Why It Matters
Medical records	Wounds, rashes, fractures	Train doctors, track healing
Surveying	Land boundaries, building sites	Permanent record, dispute resolution
Engineering	Machine parts, constructions	Enable remote replication
Botanical records	Medicinal plants, crop diseases	Accurate identification
Forensics	Crime scenes, damage	Evidence preservation
Training materials	Step-by-step processes	Teach without the teacher present
Archival	Documents, maps	Permanent backup copies

Archival Storage

Properly fixed and washed photographs last centuries. Poorly handled ones fade in months.

1. Wash prints in running water for at least 30 minutes after fixing
2. Dry flat on clean cloth, emulsion side up
3. Store in a cool, dry, dark location
4. Interleave prints with clean, acid-free paper (well-washed rag paper)
5. Never store photographs in direct contact — emulsion can stick to the back of another print
6. Keep away from sulfur-containing materials (rubber, wool, certain woods) which tarnish silver

What’s Next

Photography opens pathways to more advanced information technology:

• Printing — Photographic techniques enable photomechanical printing, reproducing images in printed materials at scale
• Data Storage — The concept of encoding information in light-sensitive media extends to microfilm and other data storage
• Optics and Microscopy — Attaching a camera to a microscope creates permanent records of microscopic observations

Photography — At a Glance

Simplest camera: Pinhole — wooden box, 0.4 mm hole, zero optics required Key chemical: Silver nitrate — dissolve silver in dilute nitric acid Best emulsion: Silver bromide in gelatin on glass plates (dry plate process) Developer: Pyrogallol or gallic acid in water with sodium carbonate Fixer: Sodium thiosulfate, 200 g per liter, 5-10 minute soak Exposure (bright sun): 2-15 seconds with dry gelatin plate and medium aperture Darkroom safelight: Dim candle behind two layers of deep red cloth Critical step: Wash prints 30+ minutes after fixing to prevent fading Best starting process: Dry gelatin plate — prepare in advance, most forgiving Safety: Silver nitrate stains permanently; avoid mercury-based processes