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The Cyanotype Process
by Christopher James
Here are some excerpts:
Cyanotype is an ultraviolet (UV) sensitive contact printing process that uses transparent, translucent, or opaque objects to make cyanotype photos on cloth or paper. The blue color of the cyanotype print is the result of the reaction of ferrous ions to the photo reduction of ferric ammonium citrate in combination with potassium ferricyanide. The cyanotype image is highly stable but can be degraded by something alkaline, such as sodium carbonate or perspiration. It will also fade, like most things, if exposed to strong direct sunlight over a period of time. Should you experience this fading, your image can generally be restored to its original blue intensity by storing it in a dark environment for a short time. Contrary to popular lore, the cyanotype print can be controlled in process to yield wonderful and technically exquisite images. The prints can also be toned in a wide variety of ways to provide alternatives to the color blue.
The Chemistry: There are two principal chemicals employed in the traditional cyanotype formula, and these are mixed together in equal parts to create a working sensitizing solution that will be applied to paper with a brush. They are: Part A, ferric ammonium citrate and Part B, potassium ferricyanide. Neither of these chemicals poses a serious health risk unless you are one of the very few people who may have an allergic reaction to the chemistry. Ferric ammonium citrate is often found in iron and vitamin supplements and Potassium ferricyanide is a stable compound that only becomes a risk if it is heated beyond 300°F
The cyanotype is a contact printing process like a photogram. As is the case with other non-silver processes, a cyanotype sensitized paper or cloth is exposed with sunlight or an ultraviolet (UV) light source and will require a negative(s) that is the same size as your intended print. I have had success with a wide assortment of negative types and can usually get a good-looking print by adjusting the way I work to fit the negative’s potential. This is one of the primary reasons that the process is such a great one to begin learning alternative techniques with, because success comes quickly to the rookie. I really do not have a specific general recommendation for a cyanotype negative. I’ve heard a lot of advice that recommends using a negative that would print well on a paper grade of 0 to 1 (indicating a fairly high-contrast negative density of about 1.5 to 1.7) and that this particular type will do well with using a standard A + B sensitizing formula. This is true, but the same success can come from negatives that do not specifically meet this recommendation. My best advice is to make a nice negative and learn the process with it. Paper and Fabric Surfaces Almost any type of paper or fabric can be used in the cyanotype process. Generally speaking, the best paper to use for a single image will be a quality hot or cold press paper like Arches Platine, Fabriano Artistico, Lana, Arches Acquarelle, Saunder’s Waterford, Somerset Book, and Crane’s Platinotype. These papers are neutral pH (in the middle of being acidic or alkaline) and already have a good sizing built into them during manufacturing. They are also specifically made to withstand the rigors of extended immersion times in liquids. Other paper options, some of them esoteric, that withstand the rigors of wet processing are those such as the 22˝230˝ Gampi Torinoko and Hahnemuhl etching paper that you can purchase by the roll. There are a wide variety of rice papers available at well-stocked art supply stores, and I recommend buying small pieces to test before committing to large amounts. One recommendation that I read about was a roll paper, 18˝250’, that was simply labeled Oriental Rice Paper for Sumi. The paper was tenaciously strong in water.
A FEW WORDS ABOUT THE SUN Before we begin exploring all of the alternative processes that follow in the book I want to mention the sun as the best light source you can use for contact printing. Unless you are working in a cold and dark climate most of the year, in which case you might think about becoming a poet, the sun provides the most efficient and least expensive means of exposing your contact negatives in printing frames. However, serious or cold climate based alternative process printers swear by a UV exposure unit because they feel it provides a consistent and controllable light source year round. Why is sun best? It’s free, really bright, and nothing can come close to the good feeling you’ll have sitting around outdoors printing with your friends and family. Secondly, in the summer your exposure times are short and pleasant, and it is easy for you to monitor your progress. Outside, the light is bright enough to read the exposure of your edges and their density. Simply observing the changes will give you a lot of information because alternative process exposures are easily determined by this evaluation method. When you think that you are close to being done, it is a simple matter of picking up the frame and moving into a shaded area to check on the details of shadows and highlights. Of course there are variables with the sun that you will not find with a UV printer unit. The time of year, time of day, humidity level outside, and overall atmospheric conditions will all have something to do with your exposure. A misty and foggy day that makes you squint your eyes will often be an ideal one to print. Use the winter to enrich your life with other interests or make (see Appendices) or buy a UV exposure unit equipped with daylight tubes. Do not waste your time with filtered “black-light” tubes like the ones that make Jimi Hendrix posters come to life because they are very inefficient exposure sources. You may, however, successfully use an unfiltered UV tube.
Exposing the Cyanotype When your coated and sensitized paper or fabric is completely dry, place your negative in contact with the coated emulsion and double check to see that it will read correctly when it is completed. The negative that you use will work very well if it has an average negative density in the range of 1.4 to 1.6. Be aware that you will be losing a considerable amount of density in the wash and development stages, so it is important that your highlights are able to print. Next, load the negative and coated paper into your contact frame so that the negative is next to the glass of the contact printer and the coated paper is behind the negative. Be sure that the hinge part of the frame back straddles the negative/coated area so that you can undo one side of the frame during exposure if you wish to check on your progress without losing registration. The most common problem in cyanotype printing is underexposure, where the highlights and middle values wash out in the water development. It is not a question of whether they will wash out, but to what degree. Depending on your negative, you will have a short or a long exposure, with darker negatives obviously taking more time than lighter ones. In summer sunlight, a short exposure might last 1 to 3 minutes, and a long one up to a half an hour. It is generally a good idea to make a test print. There are several ways to test exposure time during the exposure. When I am teaching a workshop class how to make cyanotype murals in the sun, I often use the students as photogram objects on a sensitized bedsheet. During the exposure I periodically lift their fingers to check on the comparative densities. This allows me to see what the base emulsion is doing in adjacent comparison to the open exposure next to the student’s finger. Unless they are sweating a lot, this is a good method of calibration. In a contact printing frame, I often place a small opaque object on the glass so that it covers a separate swatch of emulsion that I had added to the bottom of the paper during coating. By quickly lifting the opaque object I can determine where the exposure is and how long I have before the processing begins. As you will discover, overexposing a cyanotype is a difficult thing to do. A test strip can be easily made by coating a piece of paper with the sensitizer, drying it completely, and placing a negative in contact with the emulsion. Put the sensitized paper and negative in your contact frame and lay a series of opaque strips over the coated test piece. These strips will be removed, one at a time, at predetermined intervals and then processed for the information. You can also use a transparent step wedge for this task, but I feel the negative’s information from the test is often more important than how many gradations you might achieve with it. When the test exposure is done, process it in tap water until the whites have cleared and there is no evidence of yellow in the wash water. Then quickly blow-dry the strip, and you’ll get a rough idea of approximately what the best exposure will be. Be aware that cyanotype print values will darken over a period of days as the print oxidizes. You can accelerate this oxidization by immersing the washed print in a weak solution of hydrogen peroxide. Cyanotype is a printing-out process, so you can examine your exposure as you go, providing you are using a hinged contact printing frame. I generally like to see, in a predevelopment examination of the exposure, highlight detail that is a great deal denser than I would be happy with in a finished print. Occasionally, I want my deepest shadow details to have a nearly solarized look (the density has begun to reverse itself and is transforming to a lighter, almost metallic-negative-gray). I also watch the outside-coated borders that have no negative covering them. Often the best cyanotypes will be realized when the outside borders have reversed themselves to a near silvergray. Another general piece of information is that thicker papers often take a bit longer to expose than do thinner papers. Always write down your exposure time on the paper so that you can evaluate your progress over the course of a printing sessionJudy Seigel has suggested a technique where the exposure is stopped halfway through the exposure and then resumed to completion after a wait of several minutes. She reports that this interrupted printing results in noticeably better shadow details and separation without losing highlight or D-max integrity. I haven’t tried this technique in a formal experiment yet, but Judy’s suggestions are always worthwhile, and this may be another good control option to use.
Development: Water or Acid
Traditionally, the cyanotype is developed out in a water bath. This is the least complicated step possible and is the preferred development by most everyone who works with the process. The one shortcoming of water development may be a moderately limited tonal scale. An alternative development process, one that often produces a longer tonal scale, is the use of diluted acidic solutions such as distilled white vinegar or acetic acid. The nice part of this alternative is that the tonal range of values will be extended without having to lengthen the exposure. The downside is that by trading for a longer tonal scale you will often lose on the comparative highlight to shadow contrast in the print. You might think of an acid or vinegar development bath as one that turns the cyanotype into a soft graded paper. The simplest solution to begin experimenting with would be household white vinegar, which is generally the equivalent of a 5% concentration of acetic acid. White vinegar can be used straight from the bottle or diluted with water to give you more flexibility. In its pure state, it is worth about 2 to 4 levels on a step table. Here are a few signs to look for if you decide to use vinegar as a development option. ◆ White vinegar out of the bottle: A significant increase in the range of values (2 to 4 steps) but a relative decrease in the contrast. This might be a good formula for negatives that are hopelessly too high-key. A hydrogen peroxide “oxidation-hit” will have little effect on this straight vinegar developed print. ◆ Vinegar and water 1:1: Some of the image’s highlight crispness begins to return without a loss in the step table. Hydrogen peroxide has a negligible effect in deepening the blue in the print. ◆ Vinegar and water 1:3: A 2 to 3 step increase in midtone values, better highlight detail, and the hydrogen peroxide adds a little “intensification” to the blue. ◆ Vinegar and water 1:5: Still a pretty decent range in the additional steps and the highlights are better. Decent D-max (maximum density) equal to the other prints in the test sequence, and the hydrogen peroxide has a modest effect. Using Mike Ware’s New Cyanotype Process, explained later, the effects of vinegar development are less distinct. That fact is somewhat irrelevant if you are using Ware’s formula, which has a longer and similar tonal scale and a softer look to the overall image. Ware’s process does employ an acid development that has a softening impact on the contrast. Acid Post development Bath Another alternative in developing cyanotypes for additional tonal range is a technique of rinsing your water developed print in a mild acid bath following the development. Adding this acid bath step will often result in an intensification of the darker values while reducing the lighter ones. Traditional manuals, such as the Kodak Encyclopedia of Practical Photography, suggest a postdevelopment bath of 4 to 5 drops of hydrochloric acid per 1,000 ml of water for a few minutes. I have also heard of cyanotype artists who use weak solutions of citric acid, both chemical and natural, in this step. For fun, try squeezing a few lemons intoWashing and Oxidization After exposure and development, wash your developed cyanotype print in running water for 5 to 15 minutes or until the highlights have cleared to white. You should no longer see any yellow-green coloration in the water. Shorter washing times may leave ferric salts in the paper. Too long a washing time will cause both fading, through a pigmentation loss, and a decrease of highlight details in the print. If you need instant gratification, try this: After the first wash, remove the print from the water and add a splash of drugstore grade hydrogen peroxide to the water bath. Re-immerse the print and watch the blues go to an immediate and intense deep blue. This action causes the highlights to appear super white because of their relationship to the dark blues. This intensification “trick” is everyone’s favorite. Really, though, all that is happening is that you are accelerating the oxidization of the iron in the print that would happen naturally in a few days without this step. Don’t forget the wash stage after being thrilled a water bath and note the effect. You will likely see a bit of clearing and a marginal intensification of darker valueA 1% to 5% solution of oxalic acid can be used (1 to 5 grams of oxalic acid to 100 ml of water). This solution is particularly successful for spotting blue stains out of highlight areas. Take all necessary precautions when using oxalic acid because it is toxic. If your print is overexposed (which is pretty hard to do), mix up a solution of sodium carbonate, approximately a pinch to 1,000 ml of water, and immerse your image in it until it begins to fade. Watch for the first signs of yellow. Too strong a concentration or too long in the sodium carbonate solution will have a serious bleaching effect. If you feel you went too far with this, you can consult the toning section for techniques on where to go next. Tannic acid would be a likely option. If you opt to do nothing at all, save your overexposed cyanotype for a Blue-Van-Dyke print or a gum or simply throw it out and do a new one.
Toning the Cyanotype: There will be times when you simply do not want a blue image but still want to use the cyanotype technique due to its flexibility and simplicity. The following are some formulas for changing the color of cyanotypes once they have completed the final wash. In general, it is a good idea to overexpose your prints if you intend to tone them. Many of the following formulas utilize sodium carbonate or ammonia, which tend to radically reduce print density if the solutions are too strong.
A word of encouragement—many times the formulas will not work as you want them to due to water types, contamination, time of year, etc. Take these formulas with a grain of salt (sorry, bad pun) and adapt them to your own aesthetic. Very often, during workshops, I will simply pour and sprinkle formulas together to reinforce the idea that the results from these toning suggestions are not set in stone, either alone or in combination with other toners. Besides, what have you got to lose? The process is simple, inexpensive, and accidents often become individual and unique techniques. There is the issue of permanence to consider. The cyanotype, in a pure Prussian-blue state and handled correctly, is permanent and one of the most stable alternative processes. The toning steps change the chemical composition of the cyanotype image, and it is occasionally questionable if all of these formulas can be described as “permanent” after the fact. I have found virtually no deterioration in the images I toned with tannic acid over 20 years ago. This is not the case with images done during group toning demonstrations, where inadequate washing times between steps are often the rule. It is a good idea to dry your cyanotype prints before to The Big Thrill Hydrogen peroxide (3% drugstore grade) added to water will seem to super “intensify” the blue in your cyanotypes. The actual effect is simply an accelerated oxidation of the iron. This intense blue will occur eventually, given time, in any well-processed cyanotype. Hydrogen peroxide can be used immediately after the yellow has been washed out of your print. Mix it casually and without fear, because this chemical is used to clean wounds and as a mouthwash. Removing Blue: Yellow Toning There are several chemicals that will alter the intensity of the blue in your cyanotypes. As mentioned, hydrogen peroxide, oxalic acid, and sodium carbonate will all cause the blue to change, as well as solutions of chlorine bleach, sodium sulfate, sodium silicate, trisodium phosphate, and commercial laundry soaps. You may mix solutions of these chemicals and apply them selectively to remove areas of blue, and in some cases you can alter the entire color of the print or fabric in complete baths. For example, to make a yellow and white print, make a solution of trisodium phosphate in a ratio of 1 tablespoon to every quart of water. Dissolve the trisodium phosphate in hot water in a plastic tub or tray, and immerse the cyanotype in the solution until it fades to yellow. Rinse the print with running water for 30 minutes, or run the fabric through a cold wash cycle without soap. The resulting image will be permanent. Hang them and to let them oxidize for a day or so. This
The Basic Tea Toner Buy some basic and inexpensive household tea (tannic acid) and make a very strong solution in hot water. Immerse your print in it until you have the desired tonality. Using a solution of tea as a toner is a nice way to create a duotone image. The print’s highlights exhibit a pleasant tan color while the blue takes on a slightly warmer hue. If you don’t want any blue, just go through the yellow toning stage with trisodium phosphate and then move on to the tea toning. Using green and herbal teas without tannic acid in them does not work as well. Brown Toning #1 PART A 28 ml nondetergent, household strength ammonia added to 240 ml of water PART B 14 g tannic acid added and mixed well and added to 750 ml of water Tannic acid mixing takes a little patience because it does not dissolve readily in water. Break up the clumps and keep stirring until the chemical is in solution. Immerse the washed and wet print in Part A for a few minutes or until it becomes pale. Then rinse the print for several minutes and transfer it to Part B for the conversion to brown. In all of the toning formulas, too short a rinsing time between stages is the primary culprit in the discoloration of highlights and paper base white. Black Toning #1 Immerse the print in a solution of Dektol. The stronger the Dektol solution the more intense the goldenrod color that will present itself to you. When the blue is almost entirely bleached out and converted, rinse the print for several minutes in water and then immerse it in a solution of tannic acid mixed to 30 to 50 g per 1,000 ml of water. You should see a smokey black color within 5 minutes. Wash the toned print for 15 minutes. Eggplant/Red/Black Tones Use the black toning #1 procedure and after the final wash immerse the print in the strong Dektol solution again or in an ammonia bath solution consisting of 250 ml ammonia to 1,000 ml water. Black Toning #2 PART A 3 drops nitric acid* added to 1 liter water PART B 14 g sodium carbonate added to 160 ml water (5.3 oz) PART C 14 g gallic acid added to 160 ml water Begin by immersing your washed and wet print into Part A (nitric acid) for 2 minutes. Then rinse the print for several minutes, transfer it to Part B, and leave it in the solution until the image disappears and then reappears as a very light orange image. Then rinse the print for several minutes and transfer it into Part C, where the black tones should become evident. Finally, wash the print for at least 15 minutes. Blue/Gray Split Toning Allow the cyanotype to age for a day or two and then rewet the print. Mix a solution of 3 drops of nitric acid in 1,000 ml water and immerse your print in it for 2 minutes. Then wash the print for several minutes. Next, immerse the print in a weak (a pinch to 1,000 ml of water) sodium carbonate solution until a yellow split occurs, and then wash the print for several minutes. Mix up a solution of tannic acid of 25 g to 1,000 ml water and place your print in it until a blue/gray split appears. Finally, wash the print well for 15 to 20 minutes. Red Toning Follow the directions for the blue/gray toning. Immerse the print in a light sodium carbonate solution (a pinch to 1,000 ml of water) until red and then wash the print for
Eggplant Black #1 This is a very casual kitchen formula when you don’t have a gram scale. PART A 1 to 2 tsp sodium carbonate (very flexible) stirred into solution in 1 quart water Be aware of how much sodium carbonate you use in Part A. You may find that 1 to 2 tsp is far too strong a mix for your prints. If this is the case, then either make a new Part A with a pinch of sodium carbonate or add more water to the solution. PART B 4 to 10 Tbs tannic acid added and mixed really well into 1 quart water This tannic mix is much stronger than you may need to get the job done but I have found it works for me, so include it in this formula. If you find it is too strong for your prints then simply reduce the amount of tannic acid in the Part B formula.