Elizabeth Graves examines acetic acid development upon classic formula cyanotypes and disprove the myths about developing in vinegar.
There is quite a bit of conflicting information available about the impact of acidic water upon cyanotypes during processing. I have read that acid helps clear cyanotypes, that it makes cyanotypes blotchy, that it improves or impairs contrast, that it can ruin a good print… I had my doubts about some of these claims, and so elected to perform some tests and decide if acids could be useful in adjusting my own cyanotype prints.
"Direct experimentation is the best way to learn what works best for you with your existing working practices and tools."
Selected references hint that acids can be beneficial
Part of the reason that I had my doubts about acid’s negative influence is that I used acidic water to clear prints in my earliest uses of cyanotype. The on-line article that introduced me to cyanotype basics (which is no longer available) recommended a few drops of sulphuric acid to help clear the prints. At the time, I compared clearing the prints in ordinary tap water against the acidified water, and determined that the acid seemed to speed the clearing (and resulted in more blue in the rinse water).
I have also enjoyed Richard Farber’s book, Historic Photographic Processes, which recommends the use of weak solutions of acetic or citric acid for contrast adjustment. The book provides persuasive sample step tablets showing the difference in contrast that are possible with different concentrations of acid development.
To truly know if acid could be useful to me in my working practices, I decided to try an inexpensive and readily available form of acetic acid: white vinegar.
To test the effects of acid, I used the following materials and methods:
- Paper: I used Weston Diploma Parchment for the prints.
- Emulsion formula: I used the classic cyanotype formula, 1A:1B, double coated.
- Negatives: I utilized digital negatives printed on Pictorico overhead transparency film, using an Epson Stylus Photo 1400. I do not employ any special curves.
- Exposure: I used my homemade light box, which uses arctinic black lights. Exposure times were as noted with the sample images.
- Development formula: For acetic acid development, I used undiluted white vinegar of 5% acidity, which I poured into a tray slightly larger than my prints. I used just enough vinegar to cover one print completely, rocked the tray gently, and allowed each print to develop for one minute. (I rinsed out the tray and used fresh vinegar after developing 8 – 10 prints.)
For the "control" prints, I used a tray of plain tap water and gently rocked the tray to develop the prints for about one minute. (Note that my water department advises me that our tap water has a pH of 8.9.)"
- Wash: I rinsed the prints briefly by hand, since the vinegar drains off the paper in a strange, sheeting fashion, and then washed the prints in an archival print washer with tap water (pH 8.9) for one hour.
- Dry: I hung the prints on a line outdoors, and let them dry for about 24 hours in our high ambient humidity. I then brought them inside to finish drying in a heated room.
The vinegar does two useful things in these experiments: it brings out significantly more midtone detail from my negatives, and provides a satisfying print in about half the exposure time water development requires. Water development, in comparison, provides a deeper shade of blue and higher contrast images, but requires longer exposure times. By adjusting the acidity of the water, I can adjust the levels of contrast and midtone detail in my prints without straying from the classic cyanotype recipe, and without resorting to more toxic substances (such as potassium dichromate) to adjust the contrast of my prints.
Vinegar is a simple way to adjust my cyanotypes in useful ways. I plan to use vinegar (or other forms of acetic acid) in my cyanotype printing practices more often.
Blueprint to cyanotypes – Exploring a historical alternative photographic process
by Malin Fabbri and Gary Fabbri
A well illustrated step-by-step guide to cyanotypes.
A lot more information on the process, chemicals, coating, exposure, printing, making negatives, washing and troubleshooting is available in this book.
Strongly recommended for beginners