3. Salt prints - potassium dichromate

Feb. 5, 2026

Background

Potassium dichromate is a nasty, dangerous chemical. It’s highly toxic, corrosive, and a known human carcinogen.

It also produces better contrast in salt prints, and is commonly mentioned in processing methods. Worth it?

I had to see for myself. It must be handled with care, and the water baths after processing should be neutralized with other chemicals to reduce its toxicity to the environment. I’m no chemist, so I generally try to stay away from chemicals in the darkroom that have added levels of risk, but I figured I should understand the potential benefits and effects that the chemical could have on prints should I need to utilize the effect in the future.

Process

These prints were printed 2 days after coating, which is not ideal at all. Some unexpected things came up that prevented me from processing the prints on the same day. It presumably resulted in some bad staining and probably reduced the contrast overall as well.

For these prints, I followed a more archival workflow combining elements from the process described by Christopher James in The Book of Alternative Photographic Processes and the heavily researched Salt Printing Manual by Ellie Young, who wrote a thesis on the process at RMIT University.

It goes something like:

1. Salt and Citric Acid bath - 5 min - (1L water, 30g kosher salt, 10g citric acid)
2. Water wash - 10-15 min - (water replacement 2-3 times)
3. Fixer bath #1 - 5 min - (1L water - 100g sodium thiosulfate)
4. Fixer bath #2 - 5 min - (1L water - 100g sodium thiosulfate)
5. Hypo clear - 5-10 min - (1L water, 10g sodium sulfite)
6. Water wash - 30-60 min - (water replacement several times)

While the previous process took around 60-70 min, this more archival workflow can take up to 120 min to fully process a print. Of course, you can have multiple prints running through the trays simultaneously or subsequently, but it’s a time-intensive process, especially compared to silver gelatin or simpler alternative methods like cyanotype, which can be processed in under 10 min.

Conclusions

So, what were my conclusions after this very brief foray into working with potassium dichromate? It definitely has a noticeable effect on the tonal qualities of the print, and significantly increased the contrast and tonal depth in the test prints. You can see the results for yourself below.

Is it worth it? For most prints, no, I didn’t enjoy the added stress of working with a highly toxic chemical and the added time and effort it took to neutralize the toxic baths and clean the trays.

Contrast probably isn’t worth the environmental risk that come with disposing of the processing solutions, even though they are, in reality, miniscule compared to any industrial process.

However, if I was producing prints for an exhibition or working with very flat images, the noticeable difference in image characteristics could be valuable enough to warrant the extra caution and processing effort. I need to continue experimenting with it before giving a final verdict.