Photography with iron (iii) salt

The process of making in-camera photographs with ferric salts in camera by Arpan Mukherjee.

Writer and photography / Arpan Mukherjee

Cyanotype in camera
Taken by 10X12 vageswari plate camera at f4.5/ 20min exposure.


Instead of ferrous sulphate my chemistry suppler gave me a bottle of ferric sulphate, which I was supposed to use for wet plate developer. The bottle was black and I didn’t notice the mistake at a glance only wondering why the bottle is black. After a while realized that it is iron (III) sulphate and not iron (II) sulphate.

The black bottle raised a question in my mind that whether Ferric sulphate is sensitive to light or not. I did a test by applying ferric sulphate solution on paper and with a negative expose it to sun. It took long time but when developed by potassium ferricyanide got a positive image which was blue though it took long time to expose.
This excitement immediately reminds me ‘Eder Table’ about photo sensitivity of various iron salts. I could recall that some where I have read that any ferric salt mixed with organic acid became sensitive to light. I jumped in to exploring some of the ferric salts and its characters. In the first phase I mixed Oxalic acid with ferric sulphate and developed the image after exposure to sun. I have never seen cyanotype print been over exposed in six minutes. So I reduce the time of exposure to 45 sec to one min, and got good result. I was very excited to discover these phenomena and also found a very sensitive emulation. The similar experiment I have done with Ferric Chloride, tartaric acid, oxalic acid and it worked as well.

After words I found that the prints been darken. There was a need to fix the print that I realized. Later on found a very light solution of hydrochloric acid will do that.

The excitement was not over when I also started thinking to click photograph with this solution. By this time I made my own camera using magnifying lens for some other photographic project and I was using X-ray film to click images. Instead of X-ray film I started using paper, coated with the new solution and got the result though it was really a long exposure. But the interesting thing is that I clicked the image by using iron not silver. It took 20 min to expose, and got a very good negative, made the positive using digital methods. I also used my 10”X12” wet plate camera to click and got a similar result.

iron salt image
Taken by 10X12 vageswari plate camera at f4.5/ 20min exposure.

Hence it is interesting to note that iron (iii) salt mixed with Oxalic acid could easily be reduced by the act of light to iron (ii) salt. Afterwards potassium ferricyanide has to apply to make the image visible. On further research I found that for printing the chemistry could be changed a bit which I’ll explain later and for clicking photographs this simple method could be used.

Earlier I was also experimenting with cyanotype toning and by hunting Indian traditional knowledge in the field of textile I found some tropical fruits which are capable to provide beautiful colours. I am mentioning this in the context of clicking photographs because toning of negatives gives a reach positive as the blue converts to black brown.

In this article I’ll mention the three stages separately like process of making photographs, Process of printing and process of toning using Indian traditional knowledge.

Process of mixing the chemistry

Chemicals needed:

  1. Ferric (III) sulphate: 8 gr
  2. Oxalic Acid: 10 gr
  3. Potassium Ferricyanide: 25 gr
  4. Hydrochloric Acid: few drops
  5. Distil water: 1 Lit
Cyanotype taken in camera
Taken by 10X12 vageswari plate camera at f4.5/ 20min exposure.


Mix the ferric sulphate with 50ml of water and oxalic acid to 50 ml of water. It will take some time to dissolve the ferric sulphate salt completely. Use a glass rod to dissolve the salt. Now In the dark room using a red light mix Oxalic acid with Ferric Sulphate using a glass rod. Initially it will be cloudy, Keep it in the dark for 30 min and a green colour solution will be available. Remember this is a photo sensitive solution; hence keep it in a dark glass bottle.

Note: in this formula the ratio of Ferric Sulphate and oxalic acid will be 4:5. Instead of ferric sulphate one can also use ferric chloride and the ratio will be 4: 6.25. Ferric chloride is a corrosive material and absorbs water from the atmosphere very fast though it is essay to mix with oxalic acid and doesn’t get cloudy while mixed with oxalic acid.


Mix 25 gram of Potassium Ferricyanide to 500 ml of water. Keep it in a tray. It is a 5% solution and one can keep it in a dark bottle.


Mix around 10 ml of hydrochloric acid to 1 litter of water.

Warning: Don’t ever in any circumstances mix the developer with any acid. It is dangerous. Please go through MSD.

Iron salt image
Taken by 10X12 vageswari plate camera at f4.5/ 20min exposure.

Process of making photographs

In the darkroom apply the above mentioned solution on paper (any paper could be used) and make it dry by using hot air. Put the paper in the dark slide box or lode other ways to the camera. As it took long exposure so select the subject keeping the nature of the emulation in mind. I found landscape, architectures, cityscapes are ideal for it. In a sunny day it takes about 20 minutes (it is according to the condition here in India, the time is variable and hence one has to explore) exposure when the aperture is 4.5 on my 10X12 vageswari camera with a ‘carl zeiss tessar’ lens. If you don’t have a wet plate camera than there are other alternatives are available. Go through ()this web site and make your own camera. My first experiments were done through homemade box camera following the design published in ‘Afghan box Camera’ website using a magnifying glass as lens.

After the exposure get the sensitive paper inside the darkroom. At this point no image will be visible on the paper until one float on the developer surface image side down. Almost immediately the image will be visible and it will be in blue. Keep it for a minute in the developer surface and put it in a tray of water. And then put it in the tray of fixture. Keep for 2 minutes while rooking the tray. Finally clean with water and hang it to dry.
Here one will get a negative which can be scanned and inverted in to positive by using computer. Research is still on to make a transparent negative which could be printed by using alt methods.

Printing with Iron Salt

In the case of printing everything are quite similar to the earlier version. Only I have changed the chemistry a bit. But the emulation mentioned above could also be used for printing which is faster than this which I am going to mention here.

Materials and chemicals needed:

  1. Ferric (III) sulphate: 8 gr
  2. Oxalic Acid: 10 gr
  3. Ammonium Hydroxide
  4. Potassium Ferricyanide: 25 gr
  5. Hydrochloric Acid: few drops
  6. Distil water: 1 Lit
  7. PH paper


The mixing of ferric salt with acid will be in the same manner I have mentioned earlier. (Solution A) After that one need to add ammonium hydroxide drop by drop until the PH coms to normal that is 7. On the other hand make a 10% solution (Solution B) of Potassium Ferricyanide by adding 10 gram of the salt to 100ml of water.
Now mix equal amount of both the solution A & B which makes solution C. This solution has a short life so don’t mix a lot at a time.


Apply this solution C on the printing paper like cyanotype process. And expose for 3 minutes under sun or uv light bank. Unlike the earlier methods here the image will be visible and develop it in water, fix it afterwards. Again clean the print in water and hang it to dry. Addition of ammonium hydroxide make it little slow but it is more user friendly.


While doing cynotype I was keen to make it black. Looking for toning methods found tea/ coffee along with tanic and galic acid formula for the purpose. I was not so happy with thouse result and started searching other chemistry and formula which can converts my blue to black or deep brown.

In this process I went to the textile department of my university and asked the professor about the methods of ‘Kalamkari’ which is a traditional method of vegetable dying of textile materials. In these methods I knew that they use iron mixed with jagary and water. The materials kept for 15dayes and then make the drawing or print using block on pre dyed cloth with a fruit called Haritaki in Bengali (Terminalia chebula: it gives black colour on the cloth while it reacts with the iron jagary solution.

Coming back to my studio I tried haritaki soked in water overnight and boiled to get the extract of it. Use it with cyanotype print with regular bleaching methods and it worked almost immediately with a superior result.


Take 250 gm of haritaki, add 500 ml of water and keep it overnight. Next morning boil the fruits and add 500ml of water to make it one litter.  Add 20 ml of alcohol to preserve the solution. While toning a print of A4 size add diluted solution of haritaki in 1:2 with water. Keep it in the tray for the desired tone.

Arpan Mukherjee is an associate professor of printmaking, visual art at Visva Bharati University, Santiniketan, India. He has received BFA & MFA in printmaking from VBU, Santiniketan in 2001. He has started his career as an artist and took photography as a major medium of practice. He is one of the earliest researchers on alternative photography in the country and has developed medium like gum dichromate, cyanotype, salt print, wet plate collodion, silver gelatin emulation etc, according to Indian climatic conditions. He did extensive research on 19th century photography methods and materials since 2001 and incorporated in to mainstream visual art arena. His works are mainly related with socio-economic, political issues. He works in documentary / conceptual format with a satirical approach. He is using the 19th century photographic and digital mediums according to the requirements of his works. He has participated numbers of international and national level exhibitions and workshops. He has given lectures on photographic history, practice and his own works nationally and internationally.
You can contact Arpan on the website: or by email: arpan.mukherjee (at)

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