Ethanol

SolventC2H5OHCAS: 64-17-5
Ethanol
Image: Bryan Derksen — Public domain

Physical Properties

Also known as: Ethyl Alcohol, Grain Alcohol, Denatured Alcohol

Ethanol (ethyl alcohol, C₂H₅OH; CAS 64-17-5) is the versatile organic solvent of photographic chemistry — used as a co-solvent in collodion, as a cleaning agent for equipment and negatives, as a solvent for organic developing agents that dissolve poorly in water alone, and as a final-rinse accelerant for rapid film drying.[1] For darkroom purposes, both denatured alcohol (with methanol or MEK added to prevent drinkable use) and USP-grade absolute ethanol are suitable; denatured alcohol is dramatically cheaper and works identically for all non-medical applications.

Photographic uses

  • Collodion co-solvent: Ethanol + diethyl ether in roughly 1:3 ratio dissolves nitrocellulose to produce the collodion photographic coating. Ethanol's slower evaporation vs ether controls the gelation kinetics on the plate.[2]
  • Organic-sensitizer solvent: Phenidone, dimezone-s, and similar organic developing agents dissolve more readily in ethanol than in water. A typical mixing protocol dissolves the agent in a small volume of ethanol first, then adds the ethanolic solution to the water-based developer.
  • Equipment cleaning: Ethanol removes chemical residues, dried developer stains, and silver-salt deposits from glassware, trays, and counters. Evaporates quickly without leaving residue.
  • Film drying accelerant: A final rinse with 10–20% ethanol in water dries film noticeably faster than plain water and reduces drying marks.
  • Negative cleaning: A lint-free cloth moistened with ethanol removes fingerprints and dust from negatives before scanning or contact printing.

Practical notes

Supplied as denatured alcohol (the cheapest photographic grade — typically 95% ethanol + 5% methanol or toluene denaturant), USP absolute ethanol (99%+, ~$50/L), or 95% ethanol (the azeotropic form that's easier to obtain pure). Denatured works for every darkroom purpose except direct skin contact with sensitive individuals — the denaturant is mildly toxic.

Absorbs water from air: anhydrous ethanol gradually becomes 95% on open exposure. The 95% form is the stable-in-air equilibrium and is adequate for photographic work.

Related compounds

Isopropyl alcohol substitutes for ethanol in many cleaning and final-rinse applications; slightly different solvent properties. Diethyl ether is the collodion co-solvent paired with ethanol.

Safety Notes

Acute hazards

Ethanol's hazards are dominated by flammability:

  • Highly flammable liquid (H225): flash point 13 °C.
  • Mild eye irritant.
  • Low acute toxicity by ingestion at darkroom exposure (denatured alcohol is poisonous if substantial quantities are swallowed, but that's not a realistic exposure for photographic work).

Fire & reactivity

  • Flash point 13 °C — ignitable at normal room temperatures.
  • Vapor is heavier than air and pools at the floor, though less dramatically than diethyl ether.
  • Incompatibilities: Strong oxidizers (peroxides, permanganates, nitric acid).

Storage & handling

  • Personal protective equipment: Gloves and safety glasses for bulk handling; not required for typical working-volume use.
  • Ventilation: Normal darkroom ventilation is adequate for working quantities. Use local exhaust when pouring bulk ethanol or mixing concentrated collodion.
  • Storage: Tightly sealed metal or glass container in a flammable-liquids cabinet. Keep away from ignition sources.

First aid

Consult the full Sigma-Aldrich Safety Data Sheet for authoritative first-aid instructions.[3]

  • Skin contact: Rinse with water; mild drying is the only typical effect.
  • Eye contact: Flush with running water for 10 minutes.
  • Inhalation: Move to fresh air; seek medical attention only for substantial exposure.
  • Ingestion (denatured alcohol): Rinse mouth; seek medical attention for any substantial swallow (denatured alcohol contains toxic methanol).

References

  1. BOOK Haist, Grant. Modern Photographic Processing, Volume 2 1st ed. John Wiley & Sons, 1979. ISBN 0-471-04635-X. ↩
  2. 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. ↩
  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