A Non-Silver Manual: Cyanotype

The chapter called “Cyanotype” of Sarah Van Keuren’s book “A Non-Silver Manual: Cyanotype, Vandyke Brown, Palladium & Gum Bichromate with instructions for making light-resists including pinhole photography”.

Read the previous section of this book.

In England in 1842, just three years after the official invention of photography, Sir John Herschel coined the word ‘cyanotype’ (cyan from the Greek for blue and type meaning print) for a process he invented in order to make copies of his astronomical calculations. His friend Anna Atkins learned the process from him and in 1843 produced a volume of photograms of British algae that is now recognized as the first photographic book. Looked down upon in the 19th century as a vulgar means of cheap reproduction, the blues and other hues of cyanotype are now treasured for their vibrancy and permanence.

My grandmother, over one hundred years ago, learned about the masterpieces of European painting through cyanotypes (contact-printed from view camera negatives) that were distributed to her high school class. Her set of cyanotypes, still in excellent condition, was glued into several notebooks and surrounded by her handwritten notes. It must have been a shock for her when eventually she saw the paintings in color. Some of these early reproductions are mournfully appealing in their fine blue complexity.
The cyanotype process is based on the fact that upon exposure to sunlight or other actinic light, ferric ammonium citrate, a light-sensitive iron salt, is reduced to the ferrous state and turns blue in the presence of another iron salt, potassium ferricyanide.

Part A: The first part of the cyanotype solution is ferric ammonium citrate. (see under ArtChemicals.com in “Resources”). This iron salt is not especially toxic and was in fact prescribed long ago as a dietary iron supplement. The kind that we use is a bright green, almost chartreuse, powder that should come in a light-proof brown jar (or be stored in darkness) with a tight-fitting lid to prevent moisture from turning the hydrophilic light green powder into a sticky and, later, hardened dark green glob.

To prepare this part of the solution, pour 8 ounces of distilled water into a wide-mouthed container. Carefully spoon 50 grams (a little less than 2 ounces) of the powdered ferric ammonium citrate into a paper ‘boat’ on a scale and then pour the iron salts into the distilled water slowly, stirring as you pour. After a week or so a moldy scum will begin to form on this solution. In the early stages, it can be ignored with no ill effects in printing. Later it can be lifted or strained out of the solution. You can prevent the mold from getting started in the first place by adding a few drops of formaldehyde to the solution, but formaldehyde is toxic and, unless it is already on hand for other purposes, it might be wiser to do without it in a home studio and to strain the solution instead.

Part B: The second part of the solution is potassium ferricyanide which turns blue where it is in contact with ferrous ammonium citrate. Since potassium ferricyanide (not to be confused with potassium ferrocyanide) is a commonly used bleach for black-and-white films and prints, it can be bought at well-stocked photography stores or ordered via the internet or by phone (see “Resources”). This chemical is caustic and potentially more toxic than the ferric ammonium citrate. It should not be combined with acid because cyanide gas could be released. There are varying opinions among chemists and safety experts as to whether cyanide gas is released during the exposure to actinic light of a surface sensitized with cyanotype chemistry. Most think that it is not a problem, but to be on the safe side, step back when opening a contact frame in which a cyanotype has been exposed and do not inhale the fumes that float off the hot print.
You now have the two components of the cyanotype process which, when stored separately, will last a few years. However, if you combine the two components, the complete solution is useable for a day at most. I store my A and B solutions in recycled plastic bottles with dispenser tops. I opaque the bottles with black photographic tape and put a patch of white tape over the black on which I write the name of the chemical, a big A or a big B, and the date each solution was prepared.

To summarize:

Part A: 50 grams ferric ammonium citrate in 8 ounces (236 ml) distilled water
optional: add a few drops of 37% formaldehyde to prevent mold

Part B: 35 grams potassium ferricyanide in 8 ounces (236 ml) distilled water

Combine parts A & B in equal amounts when you’re ready to use it.
Use all of the complete solution within 12 hours or less.

Printing Surfaces

Cyanotype prints well on organic materials such as cotton, silk, linen, mulberry, and wood. It prints weakly, if at all, on synthetic materials. Contrast and sharpness vary depending on the surface of the material. A soft, unsized cotton paper such as BFK Rives will absorb a lot of the solution and, if given enough exposure, can produce a tonally rich print. On such a surface, apply the solution liberally and gently to avoid raising little tufts of fiber that could lift off your print during development and washing, leaving a snowstorm of white dots on your image. Harder, less absorbent surfaces, such as Arches Platine or Strathmore 500, require less solution and render sharper detail. No added sizing is needed for any of these papers.

Preparing to Print

Before coating paper with cyanotype chemistry, place your light-resist upon the sheet of printing paper and lightly pencil its corners so that you know the boundaries of your image area. Or, since it is not necessary to adhere to a rectangular or square format, place the negative transparency beneath the printing paper on a light table and sketch the area or shapes that you wish to render in cyanotype. Try to avoid touching the image area of your paper, especially very smooth papers such as Platine or hot-press Strathmore 500, because greasy fingerprints can repel the cyanotype solution that you will apply.

Keeping Notes

It is my practice to write notes with an HB pencil along the edges of a print, usually on the image side so that I don’t have to keep turning the print over to refer to them. Beginning in the lower left corner I note the kind of paper I am using, whether or not it has been preshrunk, and the title of the negative (with date if possible). Then I write down the first process to be applied to the paper. A typical note might read:

1) cyanotype in sun 5 minutes around noon 6/21/08

It is only by keeping careful notes that you can hope to repeat an image. During the printing process I feel I could never forget what I have done, but a week later it is difficult to recall if the cyanotype that printed so well, (now under hardened gelatin sizing and 5 layers of gum), was exposed for 5 or 10 minutes. If you can discipline yourself to keep notes, you will learn from every print you make and avoid repeating mistakes, wasting materials, and becoming discouraged.

Preparing to Coat Paper

When you are ready to apply the cyanotype solution, tape the corners of your printing paper to a clean, dry, smooth surface so that the paper doesn’t slide around. Drafting tape is ideal because it releases easily and will not tear the paper. Masking tape can serve the same purpose if you reduce its tack by repeatedly touching it to your finger or some other surface so that it doesn’t pull off paper fibers when you remove the tape. When coating a thin paper that will curl upon itself and possibly mar itself as it dries, tape the paper to a piece of glass or plexi that can be slipped into the drying rack (or if you are drying it on a line, weight the lower corners with clothespins or make some other arrangement). When coating thin cloth or porous rice paper, tape the material to glass or plexi to prevent contamination of —and possibly from—the drying racks.

Combine the A and B parts of the cyanotype solution using the minimum amount you think you will need for this printing session so you don’t waste any. More can be mixed quickly if needed. In a small graduated cylinder, combine the 2 parts of the cyanotype solution. Five milliliters of each chemical mixed together should be enough to coat 8˝ x 10˝ areas on 4 sheets of paper, depending on the paper’s absorbency. The complete solution can be poured into a shallow container that will accommodate a brush.

Brushing on Cyanotype Solution

Dip a clean dry brush (any kind of brush as long as no metal comes in contact with the chemicals) into the greenish-yellow liquid, charging it fairly liberally, and apply the solution where you intend to sensitize the paper. In a class situation do not brush the solution all the way to the edges of the paper because then it tends to creep onto the back of the sheet, which contaminates the coating area and drying screens (or clothespins) as well as your fingers. Remember that even dry chemicals can offset onto your always slightly moist fingers and from your fingers they can offset again into your eyes, mouth, food, etc. Having a chemical-free border gives you a margin of safety, as well as space for notes, signature, etc. If you wish to have blue to the edges of your paper, you can print on a larger piece of paper with clear borders and then tear or cut it down to the blue when the print is finished and dried. Or if you are using a paper with special edges that must be blue you can tape the paper to larger sheet of glass or plexi that you put in the drying area. Please carefully clean the glass or plexi when done and return it to its home.

Use a dry sponge brush to soak up excess liquid you may have brushed onto your paper; otherwise, your final print might be streaky with white patches. Orange crystals of potassium ferricyanide form as puddles of excess solution dry and mask actinic light, preventing it from creating Prussian blue on your paper. The result can be a white crystalline pattern, like frost on a window, just where you may have intended the richest blue to print. Perhaps you will find that you actually like this effect and will puddle cyanotype solution intentionally at times. Subtle puddling of cyanotype chemicals may be responsible for variations in the blue intensity of prints that have been given identical exposure times.

Dry the paper in darkness, with circulating air if possible. After about 10 minutes, go over both sides of the paper with a hairdryer. Avoid touching the coated surface with your fingers. The paper is dry if it looks flat, doesn’t feel cool on the back, and flexes easily with a slight crackling sound. If the paper is not dry, your negative could be stained or bleached by the still damp cyanotype solution (potassium ferricyanide does bleach silver in addition to making Prussian blue). Try to expose coated paper soon after the brushed-on solution is dry, but, if necessary, it can be stored longer in low humidity. If there has been a delay in exposure of coated paper under humid conditions or if the paper is not completely dry, lavender tints may appear in image highlights and contrast may diminish. Often the lavender tints disappear as the cyanotype dries.

Exposure

For printing by inspection, hinge one side of your negative to the sensitized paper with 2 small pieces of clear tape so you can lift the negative to check the exposure (like turning a page in a book) without losing registration.

Cyanotype usually requires considerably more actinic light than the other processes described in this manual. My favorite actinic light source is the sun. It is free, clean, powerful, relatively safe, and fun to use. The best times for making sun exposures year round (at least in Pennsylvania) are between 10am and 3pm — and later into the afternoon in the summer months. An efficient exposure is achieved if you position your contact frame like a solar panel so that the sun’s rays are perpendicular to the printing paper and travel the shortest distance through the glass of the contact frame. However, if you are using a windowsill you must leave the contact frame flat. Never risk the calamity of a contact frame falling out of a window!

It is a waste of time and energy to use tungsten photofloods to expose cyanotypes. Their predominant wavelength is yellow and cyanotype does not react to yellow light. What’s worse, the heat from a photoflood may crack the glass of the contact frame. Unfiltered blacklight bulbs are cool slow sources of actinic light. If you can find one these days, an old-fashioned 275w sunlamp bulb works also but takes even longer.

A pulsed-xenon or mercury vapor bulb in a platemaker (primarily intended to expose lithographic plates) is a powerful actinic light source but is not really intended for long cyanotype exposures (and, in the process, generates ozone that should be vented). The very expensive bulb may overheat and rupture unless given a chance to cool periodically.

Don’t use an old-fashioned carbon arc unless you have very good ventilation. Potentially lethal carbon monoxide is released by the burning charcoal.

Exposure times with all of these light sources depend on the density of the negative and can vary greatly. A sufficiently exposed cyanotype should look grossly overexposed and solarized before development. If you sit outside and watch a bit of cyanotype on paper (that is brushed beyond the border of the negative) respond to the actinic light of the sun, you will see the greenish-yellow cyanotype coating turn aqua-green immediately. The coating then turns deep blue. If you stopped exposing at this point, removed the negative, and submerged the paper in water, most of the cyanotype solution would probably wash off the image area and, at most, you might be left with a faint blue border around your image. A strong deep blue print results when the most open parts of the negative, that are going to print the darkest blues, have solarized to light silvery purple or light greenish gray or even beige, depending on the kind of paper used. What will end up as the deepest blue areas should look lighter than the surrounding printed-out tones.

If you are in the habit of using a 21-step film scale in your margin and wish to print to step 11, expose until you see tones printed out through step 17 before developing in water where it will lose about 6 steps.

When exposing through continuous-tone film it is important to check underneath the film for signs of solarization rather than going by the color of the sensitized paper that is not covered by the negative. To give an example, when you’re exposing a cyanotype using a film such as sheet Tri-X, you need to give twice as much exposure to get maximum density in the open parts of the negative as you do in the margins because of the inherent density of the film base plus the unavoidable chemical fogging that occurs on continuous-tone film. This extra density is referred to as film-base-plus-fog.

Development

Fill a tray with cool water for the preliminary washing of the exposed cyanotype. Slip your paper into the tray face up and rock the tray to make sure no bubbles are trapped on the print’s surface. Lift the print with tongs or gloved hands and slide it back into the tray face down. Continue lifting and flipping the print, face up, face down, for at least 2 minutes. (Change the water in the tray every few prints to get rid of the chemicals that leach into the water as they release from the unexposed areas of the paper’s surface.)

Transfer the print to a larger wash tray equipped with a tray siphon running fast enough so that it injects fresh water into the tray and pulls out used water from lower down, but not so fast that it buffets and crimps the print. A thick, soft paper such as BFK Rives, which absorbs chemicals deep into its fiber, requires longer washing than a harder, thinner paper such as single-ply Strathmore 500. Determining how long to wash the print requires judgment regarding paper strength, archival qualities, and water conservation. Certainly any paper is not sufficiently washed if water draining off the print is yellow instead of clear but there is no need for excessive washing that can actually remove some of the image as well as waste precious water.

Bleaching a Cyanotype

It is common practice to deepen the blue of shadow areas with a brief bleaching of the cyanotype — and perhaps, in the process, to retrieve overexposed details and clear foggy highlights. In the past we have immersed the cyanotype in a solution of approximately one part household laundry bleach (5% sodium hypochlorite) to 32 parts water. Because bleach tends to make paper fibers short and brittle, the print must be washed afterwards until you can no longer smell the bleach on the paper.

In Finland, sodium hypochlorite is considered so harmful to the environment that a prescription is required to obtain it. My Finnish friends suggested a dash of hydrogen peroxide as a safer alternative since it reduces to water instead of forming harmful chlorine compounds, has no fumes, and is gentler to paper fibers. I found that peroxide had the advantage of deepening the blue of the most exposed parts of a cyanotype without bleaching away any highlight detail. I have since read and then seen for myself (to my embarrassment) that peroxide simply gives us a preview of how the cyanotype will look when thoroughly dry — which is a darker blue than when first developed and wet.

In my search for a kinder, gentler bleach, I have Judy Seigel, editor of Post-Factory Photography, (see “Resources”), to thank for letting me know about bleaching with odorless and more effective sodium carbonate, commonly known as soda ash and available in the laundry section of grocery stores as ‘washing soda’. I have not yet determined its effect on paper fiber but suspect that it is less destructive.

Prolonged immersion in either sodium carbonate or sodium hypochlorite takes a cyanotype back through color changes that the print went through during exposure, but in reverse order. You may stop the bleaching process at any shade of blue, green or yellow that you fancy by pulling the print from the bleach tray and plunging it into a tray of water. A continuous-tone image will often bleach into a split-tone with gray highlights and blue shadows or yellow highlights and green shadows. This occurs because the bleaching has more impact on the thin highlight passages than in the denser shadow areas.

Richer bleached colors result when you overexpose onto a soft paper such as BFK Rives which absorbs more of the cyanotype solution than a hard paper such as single-ply Strathmore 500.

Toning with Tannic Acid & Sodium Carbonate

During prolonged bleaching, the lighter tones disappear first and eventually the entire image will turn a pale yellow or gray or vanish. These lost tones can be restored in a rosy-brown color by putting the bleached cyanotype in a tray of water laced with lithographer’s tannic acid, a light brown powder (see Bostick & Sullivan in “Resources”) that smells like instant tea mix. In the past we used to bleach cyanotypes in household bleach (sodium hypochlorite) and then bring back the image in tannic acid.

If you are using sodium carbonate as your bleach the instructions seem counter-intuitive but it works to immerse the print briefly in tannic acid (about 1/2 teaspoon to a quart of water) and then in sodium carbonate (about 1/2 teaspoon to a quart of water) and then back into the tannic acid and on to a preliminary wash tray and a final wash tray.

Wear gloves when handling the jar of powdered tannic acid and when toning prints in a tray of tannic acid in water since it stains the skin. The darkening action of tannic acid continues during the washing and drying of the print. Through experience you’ll learn to remove your print from the tannic acid bath before reaching the desired effect.

If you are using a continuous tone negative, a duotone image with rosy brown highlights and blue shadows can be gotten with partial bleaching and toning.

Discard the tray of tannic acid at the end of the toning session. It does not keep well. You can discard the tray of sodium carbonate too.

According to the artist Enid Mark, the tannin in strong cheap tea will give a warmer tone than tannic acid. She has applied bleach selectively (she used household bleach but you might try sodium carbonate) and toning with tea to achieve ‘local’ color within a print. A dry cyanotype on a flat surface can be brushed selectively with bleach and then flooded with water so that the bleach is washed out but the surrounding areas are not affected noticeably. Applying bleach to a damp or even a wet cyanotype will give softer edges as the bleach bleeds into surrounding areas. A slow transition, or gradient, from deep blue all the way to yellow can be achieved by immersing the part of the print to be lightened in a bleach bath and moving it skillfully to avoid ‘lap’ marks. Having the print damp to encourage capillary action helps to soften the effect here too. The same strategies apply to the application of either tannic acid or strong tea in areas that have been bleached to restore the original cyanotype image but in brownish tones. You should be warned that tannic acid slightly stains the white parts of a cyanotype image. Strong tea is even more likely to discolor highlights; after all, it has been used for a long time to tint white lace and crocheted doilies.

Deconstructing Cyanotype

I highly recommend Cyanotype: The History, Science and Art of Photographic Printing in Prussian Blue by Dr. Mike Ware’s (see “Resources”). After reading it, I began to experiment with the components of cyanotype, attempting an artist’s deconstruction of the medium.
The most interesting result came from coating paper with Part A, the light-sensitive ferric ammonium citrate, alone. Exposing the coated paper to actinic light through the negative produced a tan rendition of the image, which washed off the paper entirely in water. But if, instead of developing in water after exposure, Part B, potassium ferricyanide, is selectively brushed on the Part A rendition, the image instantly turns blue wherever the brush touches the image area. As you slip the paper into the tray of water, a fine veil of blue may appear where potassium ferricyanide drifts across parts of the image that you didn’t brush it onto. This delicate effect can be controlled by the flow of the water. A few students experimented with this way of working. There was some notable success mixed with a little disappointment that the blue wasn’t quite as vibrant as it is when Parts A & B are mixed, applied, and exposed together.

Read the next section of the book.


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