Glycin

Developing AgentC8H9NO3CAS: 122-87-2Shelf life: 36 mo
Glycin
Image: 0dorkmann — CC0

Physical Properties

  • Molecular Weight: 167.16 g/mol
  • Solubility (20°C): 0.2 g/L

Also known as: p-Hydroxyphenylaminoacetic Acid, Athenon, Monazol

Glycin (N-(4-hydroxyphenyl)glycine; C₈H₉NO₃; CAS 122-87-2), also called photo-glycin to distinguish it from the unrelated amino acid of the same English name, is a slow-working, warm-tone developing agent valued for its exceptional shelf life in solution and for producing warm-brown image tones on silver gelatin paper.[1] Historically important in the 1920s–1940s as the agent in "warm-tone portrait" developers and in replenished tropical-processing formulas, glycin has fallen into relative obscurity as phenidone-based developers have taken over the fine-grain territory glycin once dominated.

Photographic uses

  • Warm-tone paper developers: 5–10 g/L glycin in a sodium-carbonate-activated paper developer produces warm-brown tones directly, without any separate toning step.[2]
  • Glycin-hydroquinone superadditive pair: A less-common alternative to MQ/PQ pairs; gives warm-tone results where MQ/PQ would give neutral tones.
  • Tropical processing formulas: Glycin oxidizes slowly enough that tropical-climate processing (high ambient temperature) is feasible where metol-based developers would self-oxidize before use.
  • Replenished developer systems: Long working life made glycin valuable in the replenisher-based commercial lab era before modern stabilizers.

Practical notes

Supplied as fine white to pale tan crystalline powder. Only sparingly soluble in cold water; dissolve in warm water (40–50 °C) before adding to the rest of the formula. Stable for years in a tightly sealed dry container. Solutions keep exceptionally well — a glycin developer stock can last 6–12 months in closed glass, far longer than any MQ/PQ equivalent.

Glycin has been replaced in most contemporary workflows by phenidone or dimezone-s (better activity per gram, safer toxicology). It remains useful for workers specifically targeting its warm-tone signature.

Related compounds

Metol is a more-common developing agent with overlapping soft-working properties. Phenidone has largely replaced glycin in contemporary formulas. p-Aminophenol shares the aminophenol chemistry family.

Safety Notes

Acute hazards

Glycin is a mild-to-moderate developing agent with low-to-moderate acute toxicity:

  • Skin sensitizer (less common than metol but documented).
  • Eye irritant in concentrated solution.
  • Harmful if ingested: moderate acute toxicity; avoid skin-to-mouth transfer.

Storage & handling

  • Personal protective equipment: Nitrile gloves, safety glasses, dust mask for weighing.
  • Storage: Tightly sealed in a cool dry cabinet.

First aid

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

  • Skin contact: Flush with water for 10 minutes.
  • Eye contact: Flush with running water for at least 15 minutes.
  • Ingestion: Rinse mouth; seek medical attention.

References

  1. BOOK Haist, Grant. Modern Photographic Processing, Volume 2 1st ed. John Wiley & Sons, 1979. ISBN 0-471-04635-X. ↩
  2. BOOK Anchell, Steve. The Darkroom Cookbook 4th ed. Focal Press, 2016. ISBN 9781138959170. ↩
  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