Processes and Applications
Part of Photography
An overview of the major photographic processes — their chemistry, requirements, advantages, and best applications — to help you choose the right process for your situation and resources.
Why This Matters
There is no single “correct” photographic process. Different situations, resource availabilities, and applications call for different techniques. The daguerreotype is unmatched in detail but requires mercury and produces no copies. The calotype requires no glass but produces soft images. The gelatin dry plate requires more chemistry but is the most practical all-around process. Cyanotype requires no silver but only prints blue.
A community rebuilding photographic capability may need to start with the most accessible process (cyanotype or salted paper, requiring minimal chemistry) and progressively develop toward more capable processes as chemical production capacity increases. Understanding all the processes and their requirements allows intelligent sequencing: start with what you can do now, and build toward what you need.
This article maps the photographic landscape — what processes exist, what each requires, what each is best for, and how they connect to each other in a development sequence.
The Major Photographic Processes
Cyanotype (Blueprint)
Invented: 1842 by John Herschel Chemistry: Iron-based; ferric ammonium citrate + potassium ferricyanide Image material: Prussian blue (iron(III) hexacyanoferrate) Sensitivity: Very low — sunlight only, contact printing, 5-20 minutes Copies: Yes (contact print from negative) Resolution: Limited by base paper texture Permanence: Good in dark, dry storage; destroyed by alkaline conditions
Best for: Document copying, engineering drawings, line work, blueprint maps, any application where blue-on-white is acceptable and silver is unavailable.
Process summary: Mix iron solution, coat paper, dry, contact print in sun, rinse in water. No darkroom required for printing, though loading must be done away from direct sunlight.
Limitations: Cannot produce continuous-tone photographs with good tonal range. Color is fixed (Prussian blue). Sensitive to alkalis — even slightly alkaline water destroys the image.
Salted Paper / Silver Chloride Paper
Invented: 1834 by William Henry Fox Talbot Chemistry: Silver chloride in paper fibers Image material: Metallic silver (print-out type) Sensitivity: Low — sunlight only, contact printing, 2-20 minutes Copies: Yes Resolution: Limited by paper texture; better than cyanotype Permanence: Good if gold-toned and properly fixed/washed
Best for: The first-generation silver print: simple documents, portraits, landscape records. Good introduction to silver chemistry before attempting glass plates.
Process summary: Salt paper with sodium chloride, sensitize with silver nitrate in near-darkness, contact print in sun, fix in sodium thiosulfate, wash.
Advantages over cyanotype: Wider tonal range; neutral or warm brown-black image rather than blue; gold-toning dramatically increases permanence.
Limitations: Prints, not negatives. Must be made from some other type of negative (calotype or glass plate). Requires silver nitrate.
Calotype (Talbotype)
Invented: 1841 by William Henry Fox Talbot Chemistry: Silver iodide → silver halide → metallic silver Image material: Metallic silver in paper Sensitivity: Low — minutes in bright sun Copies: Unlimited (paper negative enables contact prints) Resolution: Limited by paper fiber — soft, impressionistic Permanence: Good if waxed, fixed, and washed
Best for: Portable field photography when glass is unavailable; situations where softness is acceptable; artistic rather than technical photography.
Process summary: Three-stage paper preparation (silver nitrate → iodize → gallo-nitrate sensitize), camera exposure, gallo-nitrate development, thiosulfate fixing.
Limitations: Paper grain limits sharpness. Multiple-stage preparation is time-sensitive. Long exposure times (minutes).
Wet Collodion
Invented: 1851 by Frederick Scott Archer Chemistry: Collodion + potassium iodide → silver iodide coating on glass Image material: Metallic silver on glass Sensitivity: Medium — seconds in bright sun Copies: Unlimited from glass negatives Resolution: Excellent — glass substrate eliminates paper grain Permanence: Excellent if properly fixed
Best for: Maximum quality glass negatives; professional-quality portraits and landscapes.
Critical limitation: The plate must be exposed and developed while the collodion is still wet and sticky — within about 10 minutes of coating. This requires a portable darkroom tent in the field. Exposure of a dry collodion plate produces no useful image. This constraint makes field use difficult.
Chemistry: Requires collodion (pyroxylin in ether and alcohol). Pyroxylin is nitrocellulose — gun cotton — and the solvents are highly flammable. A darkroom fire risk.
Gelatin Dry Plate
Invented: 1871 by Richard Leach Maddox; refined by 1878 Chemistry: Silver bromide in gelatin on glass Image material: Metallic silver in gelatin Sensitivity: High — fractions of a second in bright sun Copies: Unlimited Resolution: Excellent Permanence: Excellent if properly processed
Best for: Essentially everything. This is the recommended process for systematic photographic documentation in a rebuilding civilization. It is the balance of accessibility, capability, and shelf life that makes it the default choice.
Why it won: Plates can be made in advance and stored for weeks. Exposure times in seconds enable photographing people, moving animals, fast events. No toxic mercury or flammable collodion. Field use requires only a light-tight plate box, not a tent darkroom.
Platinum/Palladium Printing
Invented: 1873 by William Willis Chemistry: Iron sensitizer (same as cyanotype) + platinum or palladium salt Image material: Metallic platinum or palladium Sensitivity: Low — contact printing only Permanence: Essentially permanent (centuries)
For completeness: Platinum and palladium prints are the most archivally stable photographic prints known — essentially immune to atmospheric sulfur that destroys silver prints. But they require rare metals. A theoretical option if platinum-group metals are locally accessible; practically unlikely.
Choosing the Right Process: Decision Framework
Work through this sequence:
1. Do you have silver nitrate or metallic silver?
- No: Use cyanotype. It is your only practical option.
- Yes: Continue to question 2.
2. Do you have potassium bromide and animal gelatin?
- No: Use salted paper (silver chloride) for printing; calotype for negatives.
- Yes: Continue to question 3.
3. Do you need copies, or is one unique image sufficient?
- Need copies: Use gelatin dry plate (negatives + printing).
- Unique image, maximum quality: Consider daguerreotype only if you have iodine, can obtain mercury, and accept the safety risk. Otherwise use dry plate.
4. How much time can you invest in plate preparation?
- Need immediate results without advance preparation: Wet collodion (but requires tent darkroom in field).
- Willing to prepare plates in advance: Gelatin dry plate.
5. What is the subject?
- Static subject (landscape, document, specimen): Any process works. Use calotype or cyanotype if that is all you have.
- Moving subject (people, animals): Requires gelatin dry plate. No other accessible process is fast enough.
Development Sequence for a Rebuilding Community
Phase 1 (months 1-3): Establish cyanotype printing from paper negatives made by calotype. No glass required. Document copying, botanical illustration, simple photography possible.
Phase 2 (months 3-9): Develop silver nitrate production from metallic silver and acid. Add salted paper printing with silver chloride for better tonal range. Begin calotype negative-making with glass plates if glass available.
Phase 3 (months 6-12): Obtain or produce potassium bromide (from brine sources or mineral deposits). Develop gelatin from bone boiling. Master gelatin dry plate production. Enable field photography with pre-coated plates.
Phase 4 (year 2+): Refine emulsion quality, extend shelf life, develop enlarging capability, establish systematic archiving of negatives and prints.