Collodion

OtherCAS: 9004-70-0Shelf life: 12 mo

Physical Properties

Also known as: Gun Cotton Solution, Nitrocellulose in Ether/Alcohol

Collodion (nitrocellulose dissolved in ether-alcohol; nitrocellulose CAS 9004-70-0) is the coating medium for wet-plate collodion photography — the defining 19th-century photographic process that produced both negatives on glass plates (ambrotypes) and positives on black-japanned iron sheet (tintypes).[1] Between the 1850s and 1880s, collodion was the primary photographic medium; although silver gelatin had supplanted it commercially by 1900, the collodion process survives as a specialty fine-art technique with a small but serious contemporary community.

Photographic uses

  • Wet-plate collodion photography: The workflow is brief and unforgiving. Collodion is poured onto a glass plate (or japanned iron for tintype), gently tilted to coat evenly, allowed to set for a few seconds, then dipped in a silver nitrate bath to form silver iodide in the colloidal matrix. The plate must be exposed and developed while still damp — typically within 10–15 minutes of coating — which is why field collodion photographers required portable darkrooms.[2]
  • Subbing layer for alt processes: A very thin collodion pre-coat on glass or plastic stabilizes subsequent photographic emulsion coatings.
  • Specialty arts and printmaking: Non-photographic uses include fine-art drafting, medical wound sealing, and historical bookbinding — all drawing on collodion's ability to dry to a clear tough film.

Practical notes

Supplied as a clear-to-amber viscous liquid. Highly volatile solvents (diethyl ether + ethanol) evaporate rapidly, thickening and eventually solidifying the solution. Keep tightly sealed; dried collodion on the container's rim flakes off as nitrocellulose dust (see safety notes).

Composition: typical commercial collodion is 4–5% nitrocellulose dissolved in a 3:1 or 2:1 mix of diethyl ether and ethanol. The ratio and nitrocellulose concentration affect coating thickness and drying time; wet-plate collodion formulas often add small amounts of potassium iodide or cadmium iodide/bromide to the collodion before coating (these form the silver halides on contact with the silver nitrate bath).

Aging: collodion darkens and thickens with time. Fresh (pale amber) collodion gives the best negatives; aged (dark brown) collodion is still usable but requires longer exposures and produces thinner density.

Related compounds

Silver nitrate is the obligate partner reagent — collodion without silver nitrate produces no image. Potassium iodide is the halide source added to the collodion before coating in most formulas.

Safety Notes

Acute hazards

Collodion's hazards are dominated by its solvent content (ether + alcohol) and by the fire/explosion potential of dried nitrocellulose:

  • Extremely flammable: diethyl ether has an exceptionally low flash point (−45 °C); collodion solutions ignite from static electricity, flame, or hot surfaces. Avoid all ignition sources.
  • Narcotic (ether vapor): inhalation of ether causes drowsiness, dizziness, and loss of consciousness at moderate concentrations. Old surgical anesthetic — this is a real inhalation risk.
  • Eye and respiratory irritant: ether-alcohol vapor is mildly irritating.
  • Skin-defatting: repeated contact with the solvents causes drying and cracking of skin.

Fire & reactivity

  • Extremely flammable liquid (H224) — flash point below 0 °C. Explosion hazard in confined spaces with solvent vapor accumulation.
  • Dried nitrocellulose film/flakes are explosive when ignited: the dried collodion coating on bottle rims and spilled drops is a real fire hazard if ignited. Wipe dried collodion residue with wet paper (not dry sweeping).
  • Peroxide formation: diethyl ether in the collodion slowly forms explosive peroxides on extended air exposure (years). Old bottles of collodion that have been opened many times are potentially hazardous; discard commercially-stored bottles older than 2–3 years.

Storage & handling

  • Personal protective equipment: Nitrile gloves (note: nitrile dissolves slowly in ether — change frequently), safety glasses, long-sleeved clothing.
  • Ventilation: Use outdoors, in a fume hood, or with substantial cross-ventilation. Never work with collodion in a confined darkroom without dedicated exhaust.
  • Storage: Tightly sealed amber glass bottle in a cool dark cabinet. Keep away from all ignition sources — no hot plates, no pilot lights, no smoking anywhere near collodion storage.
  • Fire response: Dry chemical (ABC) fire extinguisher appropriate; water is less effective (ether vapor floats and travels).

First aid

Consult the Sigma-Aldrich SDS for the specific collodion product you're handling.[3]

  • Skin contact: Rinse with water; no medical attention typically needed.
  • Eye contact: Flush with running water for at least 15 minutes.
  • Inhalation: Move to fresh air. Seek medical attention for any loss of consciousness or persistent dizziness.
  • Ingestion: Rinse mouth. Seek medical attention for substantial swallow — ether anesthesia risk.

References

  1. BOOK Crawford, William. The Keepers of Light: A History and Working Guide to Early Photographic Processes 1st ed. Morgan & Morgan, 1979. ISBN 0-87100-158-6. ↩
  2. BOOK Farber, Richard. Historic Photographic Processes: A Guide to Creating Handmade Photographic Images 1st ed. Allworth Press, 1998. ISBN 1-58115-024-4. ↩
  3. WEB Sigma-Aldrich (Merck KGaA). Sigma-Aldrich Safety Data Sheets Sigma-Aldrich. https://www.sigmaaldrich.com/US/en/search/safety-data-sheets ↩

Reference databases

Last reviewed 2026-04-22