Oxalic acid

CAS 144-62-7 · EC 205-634-3 · C2H2O4

Also known as ethanedioic acid

Handle chemistry safely

Wear gloves and eye protection, work with good ventilation, and read the supplier’s safety data sheet before use. Hazard information here is a summary, not a replacement for it. Dispose of all photographic chemistry correctly, in line with local laws and your local authority’s guidance. Never mix waste solutions, and check the supplier’s safety data sheet before disposing of anything.

Hazards

Official EU classification (harmonised under CLP Annex VI).

Signal word: Warning

Harmful or irritant

H312 Harmful in contact with skin.
H302 Harmful if swallowed.

UK and EU rules

UK Poisons Act 1972: REGULATED poison above 10% w/w – EPP licence required for members of the public (GOV.UK list of chemicals, 3 July 2026)

Photographic uses

kallitype/ferric oxalate sensitiser additive
cleaning

Sources

ECHA CHEM substance record: Oxalic acid (100.005.123)
ECHA CHEM – C&L Inventory (harmonised CLP Annex VI and notified classifications) and legal obligations (chem.echa.europa.eu APIs: /api-cnl-inventory/harmonized|industry, /api-obligation-substance/v1)
Supplying explosives precursors and poison substances: list of chemicals (supplying-explosives-precursors/list-of-chemicals (updated 3 July 2026))

Checked October 2026.