Fifty Shades of Blue: A Tutorial on the Cyanotype Process

In addition to shooting 35mm film on vintage cameras, I also enjoying making cyanotypes of the images.  Though the cyanotype process is now used in alternative photography to make prints from negatives, it was primarily used from the mid-1800s into the 20th century as a low-cost, simple method to produce blueprints.  The process uses two chemicals, ammonium iron (III) citrate and potassium ferricyanide, instead of the typical silver halide salts used in photography; when combined, they create a sensitizer that, when exposed to light, ultimately produces ferric ferricyanaide,  also known as Prussian blue (as a piece of trivia, remember that Prussian blue was used in medicine as a sequestering agent for heavy metal poisons and is used in histopathology as a stain).

I’ve always been interested in the chemistry behind photographic processes (as long as my limited chemistry comprehension allows me to grasp the reactions).   For the chemistry geeks out there, here’s the reaction that takes place:  

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For additional information on the chemistry, please refer to the source http://www.flinnsci.com/media/456436/14-a_chemistry_and_art_connection.pdf

Now, what drew me to cyanotypes  was not only the unique blue prints, but also their use by Anna Atkins, regarded by some  as the first female photographer, to document ferns, seaweeds, and other plant-life in such works as Photographs of British Algae:  Cyanotype Impressions (1843) and Cyanotypes of British and Foreign Ferns (1853).    Atkins placed her specimens directly on the sensitized paper and the result was a silhouette effect.   Sadly, throughout my career both as a student and scientist, I gained only a minute understanding of botany; much of my exposure, from vascular tissue to hormones to plant life cycles to the titillating Casparian strip, was actually in high school by Dr. Sandy Mitra, a graduate from Cornell University who taught at BMC  Durfee High School.  Later, I would learn about the immune system of plants.  From high school to the present, I’ve always had an appreciation for my green friends (I will write about creating anthotypes in the future), but whether you want to create silhouettes of leaves or prints from negatives, this tutorial should be helpful.    

A photogram created by Anna Atkins vs. my own.

Materials: 

·         Ferric Ammonium Citrate and Potassium Ferricyanide.  (A liquid cyanotype kit containing both solutions can be obtained online from Photographers’ Formulary for $18.00.  The kit can produce an estimated twenty-four 8x10’s.)

·         Watercolor paper (recommended, but other paper works, as do textiles containing at least 50% cotton)

·       Teaspoon (or a graduated cylinder or pipette for those fortunate enough to work in a laboratory setting.) 

·         Scotch tape

·         Hake brush (recommended, but paint brushes or foam brushes are fine)

·       Transparency sheets ( used for printing negatives on) or objects for creating silhouettes (e.g., leaves, ferns, paper cut-outs)

·         Glass plate large enough to cover image to be printed

·         Running water (from a sink, for instance.  Note that hard water will affect the final image color)

·         UV light source (the Sun works great and is free, but  a UV light allows for greater predictability of exposure times)





Procedure

1.         Prepare the negatives or objects you wish to use to create the print.  If using objects, objects must be flat enough to be sandwiched beneath a glass pane; creating these silhouettes (photograms) is a great introduction to the cyanotype process, since it is nearly impossible to overexpose the image.  If using a negative to reproduce a photograph, create a negative by inverting the color of a digital image  (e.g., "invert color" in Microsoft Paint) and printing on transparency sheets; make sure to choose "transparency" for the paper type under printing options.

If you are printing on transparencies, I would recommend beginning with high contrast negatives (on the left), which are much easier to expose properly than negatives of photographs (right).

2.          Mix the chemicals in a room free from natural light:  If using dry chemicals, create a 25% (m/v) solution of ferric ammonium citrate and 10% (m/v) solution of potassium ferricyanide.   Combine the solutions in equal proportions.  If using The Photographers’ Formulary Kit, simply combine the two solutions in equal proportions—from my experience, ¼ teaspoon (1.2 ml) of each solution produces enough volume to coat about half a sheet of watercolor paper (note that the sensitized solution should be used soon after preparation).  

3.       Prepare your work area and the canvas:  Let’s avoid a mess here.  Spread some newspapers over the work area and possibly get yourself some gloves.  Now, in a dimly lit or tungsten lit environment, coat the paper as evenly as possible.    Allow the paper to dry in the dark or hasten the process with a hair dryer.

4:  Print the cyanotype:  Once the paper is dry, do not touch with bare hands.  Secure your objects with scotch tape on the coated paper; ensure that it will be possible to inspect the progress of exposure without loss of registration (for example, secure the top and a side of a transparency).   In the sunlight or under a sunlamp, place the glass frame on top of the negative/object and allow for the cyanotype to print-out—exposure will likely take 10-20 minutes, but may vary considerably depending on the intensity of the sun.  Check the print periodically, and expose until the high values have more tone than desired in the final print and shadows have begun to reverse.  Highlights will lighten upon washing; thus, an apparent overexposure is necessary.  Note that underexposed images will wash away in the next step; overexposed images will be too dark.  

I recommend exposing only one print at a time, since the time will vary for each image (i.e., do not do what I did above). Alternativey, when transparencies contain several negatives, using a thick sheet of paper, it is possible to mask the print-outs when the desired exposure is achieved.

5:   Process and dry:  When the print has been exposed, process your print by rinsing under running water for at least 5 minutes.  This removes any unexposed chemicals, ceasing the process of development.   Oxidation will also be accelerated, bringing out the blue color.  The final print can now be hung to dry.  The image is colorfast, so enjoy showing it off!

Cyanotype Toning (Optional)

Images can be toned to shift the color from a blue to sepia tone. Image obtained from www.non-silver.com

If desired, it is possible to change the typical blue cyanotype to a sepia tone by first using a bleaching agent (sodium carbonate or ammonia), followed by a toning agent (tea).  During the bleaching phase, the Prussian blue lattice is broken up by the hydroxide ion, and the
ferric iron is converted into an insoluble pale yellow-brown ferric hydroxide,
while the soluble ferrocyanide ion is washed away.  Next, the toning process is performed by soaking the print in tea, which contains tannins--based on my limited understanding of the chemistry, by mixing tannin with the iron hydroxide,  an insoluble, dark ferric tannate pigment is formed. 

Because of my little experiencing toning images, I recommend following the tutorial found on this site https://mpaulphotography.wordpress.com/2011/04/01/cyanotype-toning-the-basics/ 

My Toning Method

I've had fun experimenting with toning my cyanotypes.  A quick method that has provided interesting results for me is soaking my dried cyanotype in diluted Clorox bleach for several seconds.  Once the color shifts from blue to beige, I immediately rinse the paper under running tap water (the color will continue to fade during this time until the bleach is fully rinsed out).  To tone the image, I've found that soaking in red wine for several minutes has provided a dark beige color that I find pleasing.  I have tried toning in tea, but I find the image to be more black than brown, and not particularly to my taste.  A word of advice--if you tone and do not approve of the color, give it a quick rinse in bleach and tone again!  

My own attempt at toning. I rinsed my cyanotype in diluted bleach, then soaked the paper in red wine.