The compound is also used to
harden iron and
steel, in
electroplating,
dyeing
wool, as a
laboratory reagent, and as a mild
oxidizing agent in
organic chemistry.
Photography Blueprint, cyanotype, toner The compound has widespread use in
blueprint drawing and in
photography (
Cyanotype process). Several
photographic print toning processes involve the use of potassium ferricyanide. It is often used as a mild bleach in a concentration of 10g/L to reduce film or print density.
Bleaching Potassium ferricyanide was used as an
oxidizing agent to remove
silver from color negatives and positives during processing, a process called bleaching. Because potassium ferricyanide bleaches are environmentally unfriendly, short-lived, and capable of releasing hydrogen cyanide gas if mixed with high concentrations and volumes of acid, bleaches using ferric
EDTA have been used in color processing since the 1972 introduction of the Kodak
C-41 process. In
color lithography, potassium ferricyanide is used to reduce the size of color dots without reducing their number, as a kind of manual color correction called dot etching.
Farmer's reducer Ferricyanide is also used in black-and-white photography with
sodium thiosulfate (hypo) to minimize the density of a
negative or
gelatin silver print where the mixture is known as Farmer's reducer. This reagent can help offset problems from
overexposure of the negative, or brighten the highlights in the print.
Reagent in organic synthesis Potassium ferricyanide is used as an oxidant in organic chemistry. It is an oxidant for catalyst regeneration in
Sharpless dihydroxylations.
Sensors and indicators Potassium ferricyanide is also one of two compounds present in
ferroxyl indicator solution (along with
phenolphthalein) that turns blue (
Prussian blue) in the presence of Fe2+ ions, and which can therefore be used to detect metal oxidation that will lead to rust. It is possible to calculate the number of moles of Fe2+ ions by using a
colorimeter, because of the very intense color of
Prussian blue. In physiology experiments potassium ferricyanide provides a means increasing a solution's
redox potential (E°' ~ 436 mV at pH 7). As such, it can oxidize reduced cytochrome c (E°' ~ 247 mV at pH 7) in isolated mitochondria.
Sodium dithionite is usually used as a reducing chemical in such experiments (E°' ~ −420 mV at pH 7). Potassium ferricyanide is used to determine the ferric reducing power potential of a sample (extract, chemical compound, etc.). Such a measurement is used to determine of the
antioxidant property of a sample. Potassium ferricyanide is a component of amperometric
biosensors as an
electron transfer agent replacing an enzyme's natural electron transfer agent such as
oxygen as with the
enzyme glucose oxidase. It is an ingredient in commercially available blood
glucose meters for use by
diabetics.
Other Potassium ferricyanide is combined with
potassium hydroxide (or
sodium hydroxide as a substitute) and water to formulate Murakami's etchant. This etchant is used by metallographers to provide contrast between binder and carbide phases in cemented carbides. ==Prussian blue==