A Cuprotype is a photographic print of Copper II Ferrocyanide on paper or fabric. Jim Patterson gives us a history of the Cuprotype process.
A Cuprotype is a photographic print of Copper II Ferrocyanide on paper or fabric. Cuprum = copper in Latin and the chemical symbol for copper is Cu, not Co which is cobalt. So Cuprotype translates to Copper Print in English. Copper II Ferrocyanide is a reddish brown colour and is also called Hatchett’s Brown.
Pigment in Cuprotype (Copper II Ferrocyanide) was developed and promoted by Charles Hatchett, Fellow Royal Society, in the early 1800s as a superb brown pigment with a lilac tint(1). It was later designated Pigment Brown 9 and has been used in oil and watercolour painting.
C J Burnett coined the term Cuprotype about 1856(2) for a print of Copper II Ferrocyanide (Hatchett’s Brown) on paper or fabric. It was also called Burnett’s Copper Process. He originally used a solution of Potassium Dichromate and Copper Sulfate coated on paper, dried, exposed to UV light through a negative, washed, and toned in Potassium Ferricyanide solution.
Later, Burnett used Uranyl Nitrate with Copper Nitrate(3), to arrive at a similar print of Hatchett’s Brown. Neither of these is recommended due to the toxic, carcinogenic materials.
John Mercer, a dye chemist and fabric printer experimented with Cuprotype in about 1857(4). He used Ferric Oxalate and Cupric Thiocyanate, then toned with Ferricyanide after the removal of iron salts. Little notice seems to have occurred.
In 1863 J B Obernetter used Ferric (Iron III) Chloride with Copper II Chloride as the Sensitizer, developed with a sulfuric acid/Thiocyanate solution, then toned with Potassium Ferricyanide to arrive at the same Hatchett’s Brown pigment on paper. It was called Obernetter’s Ferro-Cupric process(3). This works, but is very slow and stains easily.
A 1978 Popular Photography How to Guide had formulas for Copper Print that used Potassium Ferricyanide as the light-sensitive agent with copper complexed with citrate. Chris Patton and Cor Breukel experimented with this process. The image was a Cuprotype.
In 2007, I updated Obernetter’s process by using a mixture of Ferric Ammonium Citrate, green and Copper II Sulfate as the Sensitizer. It is developed in Ammonium Thiocyanate/Citric acid solution and toned with Potassium Ferricyanide for the same Cuprotype image. Details at www.darkroomdoc.com.
In 2022 Jan de Jong posted prints on Photrio made with Ferric Ammonium Citrate, Copper Sulfate, and Sodium Thiosulfate as the Sensitizer, exposed to UV, washed in water and dried. Niranjan Patel recognized how this could be a new version of Cuprotype by toning with Potassium Ferricyanide. An added benefit is that a Citric Acid wash increases the density and darkens the tone.
Niranjan Patel, Peter Friedrichsen, and Frank Gorga have experimented with the New Cuprotype. Below are prints from Frank Gorga.
This is an excellent process for beginners of alt photo. It works analogously to Cyanotype:
Part A: 15 % FAC + 12% CuSO4.5H2O
Part B: 10% Sodium Thiosulfate penta-hydrate
Mix 1 volume A with 1 volume B, coat paper, dry. Expose through a negative to UV. Wash in water to remove excess chemicals. Tone in 2% Potassium Ferricyanide. Wash in water. Tone in 1% Citric Acid solution for a darker tone. Wash, dry.
In all cases, the light-sensitive agent (potassium dichromate, uranyl nitrate, ferric chloride, Ferricyanide, ferric oxalate, or ferric ammonium citrate) reacts with UV light to result in a poorly soluble Copper I compound that converts to Copper II Ferrocyanide (Hatchett’s Brown) on toning with Potassium Ferricyanide. The image on paper, cotton fabric or other support appears quite stable. I have Cuprotypes from 2007 that appear very stable in color.
- The Philosophical Magazine, 1803, vol. 14, #56, pp 359-360.
- Photographic Notes, 1856, correspondence from C J Burnett.
- Photographic Reproduction Processes, 1891, by PC Duchochois.
- The Life and Labours of John Mercer by Edward A Parnell, 1886, pp 226-228.