Daguerreotype

Historical Context

Announced in 1839 by Louis Daguerre, the daguerreotype was the first commercially successful photographic process. It produces a unique image on a silver-plated copper plate with extraordinary detail and a distinctive mirror-like surface.

Traditional Process Overview

The daguerreotype process involves:

1. Plate preparation: Silver-plated copper polished to a mirror finish using progressively finer abrasives and buffs.

2. Sensitisation: The plate is fumed over iodine until it turns yellow, then over bromine (the accelerator) until it turns rose, then briefly over iodine again, forming light-sensitive silver halides on the surface (Graphics Atlas).

3. Exposure: Plate exposed in camera. Daguerre's original exposures ran up to about thirty minutes; later improvements reduced this to several seconds.

4. Development: Plate developed over heated mercury. Mercury vapour amalgamates with exposed silver, forming the image. (Mercury fuming is the most dangerous step; see the warnings below.)

5. Fixing: Unexposed silver halides removed. Daguerre used hot saturated sodium chloride, which stabilised the image but left light-sensitive halides; John Herschel's suggestion of sodium thiosulfate removed them completely.

6. Gilding (optional but usual): A gently heated solution of gold chloride and sodium thiosulfate, introduced by Hippolyte Fizeau in 1840, is flowed over the plate. It raises contrast and makes the otherwise easily wiped-off image more durable.

Becquerel Daguerreotype

Developed by Edmond Becquerel in 1840, this variant uses only iodine sensitisation and red/yellow light development, eliminating mercury entirely.

Process

Instead of mercury development, the exposed plate is re-exposed to red or amber light (through coloured glass, or from an LED). Silver iodide barely responds to this light on its own, but the latent image formed in the camera makes the exposed areas sensitive to it, so they build up finely divided silver while the unexposed areas stay largely unchanged. The image is silver rather than the silver–mercury amalgam of a mercury-developed plate.

Advantages

• No mercury required
• Significantly safer
• Can be done with simpler equipment
• Produces subtly different tonal qualities (some practitioners prefer Becquerel tones)

Disadvantages

• Slow: iodine-only plates need long camera exposures, plus a long secondary exposure to red or amber light. No standard times exist, so expect to test
• Some report lower contrast or different tonal rendering
• Less historically "authentic" (if that matters)

The Becquerel process is the recommended approach for contemporary daguerreotypists who wish to avoid mercury exposure.

Image Characteristics

• Mirror-like silver surface
• Extraordinary detail
• Unique (non-reproducible) image
• Visible only at certain angles against dark background
• Extremely delicate—must be housed under glass

Handling and Care

Daguerreotypes are extremely fragile:

• Never touch the image surface
• Store in sealed cases to prevent tarnishing
• Handle by edges only
• The image can be destroyed by wiping or cleaning

Historical daguerreotypes are often found in protective cases with brass mats and cover glass.

Safety

Mercury Toxicity Warning

Mercury vapour exposure causes irreversible neurological damage. Symptoms may not appear until damage is severe. Some nineteenth-century daguerreotypists are recorded as suffering mercury poisoning, with symptoms such as tremors and psychological disturbance.

Modern practitioners MUST use:

• Laboratory-grade fume hood with vaneometer-verified airflow (100+ fpm)
• Mercury vapour monitoring
• Proper spill containment and cleanup procedures
• Mercury-rated waste disposal
• Regular health monitoring

Do not attempt traditional daguerreotype without professional laboratory facilities.

Recommendation

For those interested in daguerreotype, the Becquerel variant is strongly recommended. It produces authentic daguerreotype images without the extreme hazards of mercury development. Many contemporary daguerreotypists use exclusively Becquerel development and achieve excellent results.

If you are determined to work with mercury, seek hands-on training from an experienced practitioner and ensure you have appropriate laboratory facilities before attempting the process.

Further Reading

Jerry Spagnoli, Daguerreotypes (Steidl, 2006) Monograph by the leading contemporary daguerreotypist. Spagnoli's work demonstrates what is possible with the medium today.

Christopher James, The Book of Alternative Photographic Processes, 3rd Edition (Cengage Learning, 2015) The definitive comprehensive text on alternative processes, with coverage of daguerreotype history and practice.

Workshop Training Few modern practical manuals exist for the daguerreotype. Practitioners typically learn through workshops with experienced makers like Jerry Spagnoli and Mike Robinson. Hands-on training is strongly recommended before attempting the process, particularly for mercury development.

Mike Ware's website (mikeware.co.uk) Free technical papers on photographic chemistry that provide background for understanding the daguerreotype process.

Sources

• Daguerreotype, Graphics Atlas (Image Permanence Institute)
• Daguerreotype, AIC Conservation Wiki
• B-dags, how do they work?, Contemporary Daguerreotypes (cdags.org)
• Supplying explosives precursors and poison substances: list of chemicals, Home Office (GOV.UK)
• International Chemical Safety Card 0107: Bromine, IPCS / WHO-ILO
• Mercury and health, World Health Organization