Potassium ferricyanide

CAS 13746-66-2 · EC 237-323-3 · C6FeK3N6

Also known as tripotassium hexacyanoferrate, potassium hexacyanoferrate(III), red prussiate of potash

Most-notified classification only 39.18% of notifications.

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

There is no official EU classification. Shown is the classification most companies have notified to ECHA: 39.18% of notifications, 9 distinct classifications notified.

Signal word: Warning

Harmful or irritant · Hazardous to the environment

H319 Causes serious eye irritation.
H411 Toxic to aquatic life with long lasting effects.

UK and EU rules

UK Poisons Act 1972: ferricyanides are expressly EXCLUDED from the regulated "hydrogen cyanide and metal cyanides" entry

Photographic uses

Farmer's reducer (R-4a)
sepia bleach (T-7a)
cyanotype sensitiser

Used in: Kodak R-4a Farmer's reducer, Kodak T-7a sulfide sepia toner, New cyanotype (Mike Ware)

Sources

Checked October 2026.