10

Gum Bichromate Prints

Safety

Method Overview

Materials

Making the Bichromate Solution

Making a Gum Print

Tips for Making a Gum Print

Making a Full-Color Gum Print

10.1  Starting on upper left:

Edward Steichen, J. Pierpont Morgan, Esq., 51.6 × 41.1 cm (20 × 16 in.), Gum bichromate over platinum print, 1903, printed 1909–10 (1903 version was carbon print), Alfred Stieglitz Collection, 1949, 49.55.167, © 2016 Artists Rights Society (ARS), New York; Untitled (Experiment in Multiple Gum), 47.8 × 38.4 cm (18 × 15 ⅛ in.), Gum bichromate print, 1904. Alfred Stieglitz Collection, 1933, 33.43.39, © 2016 Artists Rights Society (ARS), New York; Balzac, the Silhouette—4 A.M., 37.9 × 46 cm (14 × 18 ⅛ in.), Gum bichromate print, 1908, Alfred Steiglitz Collection, 1933, 33.43.36 ©Artists Rights Society (ARS), New York; Rodin—The Thinker, 39.6 × 48.3 cm (15 × 19 in.) Frame: 79.4 × 87.6 cm (31 ¼ × 34 ½ in.), Gum bichromate print, 1902. Gilman Collection, Purchase, Harriette and Noel Levine Gift, 2005, 2005.100.289, © Permission of Joanna T. Steichen. All images courtesy of The Metropolitan Museum of Art.

Steichen is one of my favorite gum printers because his pictures are not sentimental but offer a psychological encounter with the viewer. His background as a lithographer’s apprentice at 15 years of age, training as a painter at the Milwaukee Art Students League, and time living in Europe must have opened him to new ideas, because he introduced Alfred Steiglitz in New York to the then avant-garde work of Picasso, Matisse, and Cezanne. His gum prints of Rodin contemplating his own sculpture, “The Thinker,” shows an old man stooped over in meditation. Steichen returned to the United States and, after a successful career as a “straight” commercial photographer (his portrait of Greta Garbo is well-known), eventually became the first director of a museum photography department, at the Museum of Modern Art in New York, where he curated the influential and controversial Family of Man exhibit and was the first photographer to be awarded the U.S. Presidential Medal of Freedom by John F. Kennedy.

Gum printing makes water-soluble pigments, such as gouache and watercolors, photographic, producing prints of subtle and wide-ranging colors on paper, ceramics, or fabric. Mixing gum arabic, paint, and a solution of ammonium or potassium bichromate as the light sensitizer, you can create a single or multicolored image ranging from continuous-tone to high-contrast. Gum printing also can be combined with traditional printmaking processes such as etching and drypoint, or with other photo-printmaking techniques from this book. Unlike Van Dyke, cyanotype, and palladium, gum printing creates an actual physical buildup on top of, rather than an absorption into, the substrate. Because the emulsion is delicate, your patience and a willingness to experiment are essential.

One of the earliest photographic processes to be used as a personally expressive medium, gum bichromate—also known as dichromate—printing is usually credited to a Frenchman, Alphonse Louis Poitevin, whose 1855 patent, based on experiments using carbon, were founded on tests with the light sensitivity of dichromates by earlier inventors. The English photographer John Pouncy temporarily patented the technique in 1858, for a gum-pigment-dichromate sensitizer, which, when coated on paper and exposed to ultraviolet light under a negative, selectively hardened in relationship to the amount of light allowed through the different density areas of a single negative. The other parts of the sensitizer were not affected by light due to the impenetrability of the negative in those (highlight) areas, and they washed off, showing the paper. Some historians say that the process was introduced to the art world by A. Rouille-Ladeveze, who wrote the first book on gum and exhibited “photo-aquatint” prints in Paris and London in 1894. But the method was recognized as a workable artists’ medium through the showing of gum prints by Robert Demachy. In 1897, Demachy and Alfred Maskell published Photo-Aquatint, or the Gum Bichromate Process, a book that helped spread its popularity and was founder of the influential Paris Photo Club. Simultaneously the European-born American photographer, Edward Steichen, made multicolor gum prints that he often combined with other photo-printmaking techniques (see illustration at the beginning of this chapter). Two groups devoted to admitting photography into the fine-art world, the Linked Ring in London and Photo Secessionists in New York, exhibited in a few galleries and camera clubs. Demachy, Steichen, Alfred Steiglitz, Clarence White, Heinrich Kuehn, and Gertrude Kasebïer also published photogravure reproductions of gum prints in Steiglitz’s Camera Work. These photographers preferred gum printing because it resembled a painting with its thick, malleable coating, rather than the thin, hard, smooth emulsion of the standard photographic papers, and they turned to the current vogue in painting as their inspiration. Clarence White, for instance, was known to purposely remove gum print details that might detract from a picture in the style of Japanese-influenced images made popular by painters, especially Whistler, and also Corot and the French Barbizon School.¹ The process lost its popularity after the First World War, usurped by speedier methods and abandoned by Demachy, but many artists still find it a pliable and rewarding process.

SAFETY

Bichromates (aka dichromates) can cause skin inflammation, similar to an allergic reaction, upon repeated exposure. Wear protective gloves and goggles at all times when mixing and coating bichromate as well as when washing a bichromate-sensitized print. Wear a respirator with a toxic dust filter when handling bichromate crystals.

In the European Union, the dichromates (sodium and potassium) are classified as SVHC (substance of very high concern), and the use of it will be forbidden or strongly regulated and only approved after authorization from ECHA (European Chemicals Agency) after September 21, 2017. After this date “the placing on the market and the use of the substance shall be prohibited unless an authorisation is granted.”

Store ammonium dichromate away from heat and combustible materials. Bichromates are not combustible but can add to the intensity of a fire. Do not smoke in your work space.

Bichromates can be poisonous when ingested, even in small quantities. Keep chemicals and chemically contaminated materials away from your mouth and out of the reach of children and pets. They are suspected carcinogens.

Dispose of excess solution or chemical by flushing it down the drain with a large volume of water, not in a wastepaper basket. Better yet, evaporate the excess, then take this much smaller quantity to a hazardous waste center. Here is what Bostick & Sullivan (see Supply Sources) recommend:

•  Collecting the Nasty Stuff. This step is particularly important if you are on a well and a septic system! That is not to say you should be dumping it into your municipal system, however. The first step is to collect your gum-developing run off. You may wish to collect this in a large tank or plastic garbage can.

•  Converting to Trivalent. Add sodium bisulfite, sodium sulfite, plain old spent fix, or sodium thiosulfate to the solution. The solution will turn from orange to green. Keep adding until there is no more green color and add a bunch more to ensure all is converted. It is now a much safer trivalent chromium compound.

•  Making a Precipitate of the Chromium. You want to go a step further. Now add an alkali to the solution in the tank or garbage can. You can use sodium hydroxide (plain old Draino works fine) or sodium carbonate or potassium carbonate. After the alkali is added the chromium now is converted to chromium hydroxide which can be filtered out.

•  Building the Filter Thingy. I have not attempted the filtering step on a large scale as I have not gum printed in several decades. I have however filtered tanks of solution many times before with this system. Here’s how I would approach the problem: I’d start with a small pond pump. Not a real tiny one but one that costs about $50 would be large enough to handle a 50-gallon plastic garbage can. Now buy a house size water filter. They are available in any hardware store and are usually blue plastic and are about the size of a 1 liter Pepsi Bottle and cost about $15. Next buy the fittings necessary to attach the blue plastic house water line filter to the outlet of the pond pump directly. Install a cheap paper filter into the housing ($3–$5). Do not use the expensive charcoal filter cartridges, as they are a waste of money in this case.

•  Filtering the Tank. Dunk the pond pump with the filter directly attached into the tank. Plug it in and let it run overnight. It will intake and discharge into the tank. This is less efficient than filtering from one tank to the next, but the plumbing is far simpler. I’ve used this system to filter stuff in tanks in the past. You may have to change the filter two or three times depending on the amount to filter out.

•  Disposing of the Wet Nasties. When finished, put the filters in a 1 gallon Ziploc bag and label the bag “Chromium Oxide Waste.” Take the bag to your hazardous waste disposal center.

10.2a and 10.2b Left (A): Todd Walker, Untitled, approximately 5 × 8 in. (12.7 × 20.32 cm), gum print on paper, circa 1987. Courtesy of the Walker Image Trust.

Right (B): Melanie Walker, Cucumber, 16 × 20 in. (40.64 × 50.8 cm), gum print on Somerset Satin using traditional size with formaldehyde, 1985. Courtesy of the artist.

Todd Walker and Melanie Walker are father and daughter. Although both artists may share some similar visual issues, such as photographically manipulated space, each responds in a manner that reflects his or her concerns. Todd Walker was an important teacher and artist in the resurgence of non-traditional photographic methods. For the illustration in Figure 10.2, he took photos of a person inside a fabric tube and used a positive transparency, sensitizing the paper repeatedly to build up a rich black. He then used pigments with white and, at times, mica mixed into them. Todd died in 1988.

Born with a visual impairment that left her with constant double vision, much of Melanie Walker’s work addresses living with a double reality that is in a constant state of being negotiated. With this particular work, layers of glass were incorporated into the making of the image so that some of the objects seem to float on a different plane. The initial picture was from a black and white negative and additive, selective color was incorporated through the gum printing process, as described in the instructions below.

Inhalation of gum arabic solution or powder can cause asthma, so if you spray rather than brush on gum bichromate emulsion, use a respirator over your nose and mouth.

Certain paint pigments, such as emerald green, cobalt violet, true Naples yellow, all cadmium pigments, flake white, chrome yellow, manganese blue and violet, Verona brown or burnt umber, raw umber, Mars brown, lamp or carbon black, and vermillion/sindoor, can lead to poisoning and other complications if they are ingested or inhaled frequently. Wearing a respirator, working in a ventilated area, and carefully washing your hands and cleaning your fingernails after using these pigments can prevent accidentally carrying them to the mouth and ingesting them.

METHOD OVERVIEW

1.  Paper or fabric is heavily sized and dried.

2.  Under subdued light, the substructure is sensitized with the gum bichromate mixture containing gum arabic as a colloidal binder, light-sensitive dichromate and water, and any color pigment, and then dried.

3.  The coated and dried surface is immediately placed in contact with an object or negative, and ultraviolet light is shone through the negative. The emulsion hardens and becomes an insoluble colloid in correspondence to the time between coating and using the emulsion and in proportion to the “positive” areas where light reaches it.

4.  The negative is removed. The paper or fabric is developed in water, where unexposed and, therefore, soluble, areas of color are dissolved and wash off, leaving a reversed image to dry and further harden. The image can be manipulated, removing select areas of colored gum-pigment, while wet.

5.  One coating must dry before a new layer of the same (for deeper color) or different (to alter the color) gum arabic-bichromate-pigment blend may be applied to the whole or part of the image, exposed under the same or new negative, and processed.

MATERIALS

More detailed descriptions of materials are given in Chapter 4, Creating the Photo-Printmaking Studio.

1.  Applicators. You will need two brushes: one to coat the paper and one to blend the layer. In my studio I have at least one labeled hake brush for each technique I pursue, but I especially like the hake brush for chromated solutions because the bristles are stitched and not connected to the flat wooden handle by any metal that could corrode. Even though a few hairs might shed when you first break in a hake brush, they are easy to pick off after you dry and before you expose the emulsion. Other choices include watercolor brushes, fine flat bristle brushes, and nylon paint brushes. I keep an array of widths, from 1 in. (2.5 cm) for an 8 × 10 in. (20 × 25 cm) image to wider brushes for larger prints. A foam paint roller from the hardware store is a good alternative; you need to get used to it by rolling back and forth and in cross directions to get rid of roller marks until the coating is as smooth as you want. If you use an atomizer or airbrush to apply the emulsion, be sure to wear a respirator and work in a well-ventilated area. A dry Blanchard brush (see page 91), a soft but relatively expensive badger paint brush, or a clean foam paintbrush helps blend in and buff the strokes made by the coating brush. The area you want to coat will determine the width of the brush. A small, soft, round traditional watercolor brush comes in handy for coaxing the development of the print in water. Keep the metal part of the brushes away from the bichromate, or coat the ferrule with clear nail polish.

2.  Brown bottle, opaque 35mm film canister if you still use film, or pill containers. A clean, recycled fruit juice jar or dense plastic jar is optional, in case the recipe is doubled or tripled. Are you glad to finally find a use for those empty pill containers? They are perfect for storing the mixed gum bichromate solution because they are light tight and spill-proof.

3.  Chemicals and funnel. You will need premixed gum arabic 14° Baume (“baume” refers to the density of the liquid), available usually in one-gallon (3.8 L) jugs from offset lithography/commercial printing suppliers. In addition, smaller quantities—enough to last for quite a few print sessions—are sold in art stores under the names Winsor & Newton or Grumbacher gum arabic for oil painting and from Photographers’ Formulary. These commercial brands last a long time, although I have found that if the gum ages to a very dark brown, it greatly lengthens the exposure time. Even if pure gum arabic is available and less expensive as a powder, it is time-consuming to mix and strain at the proportions of 1 oz. (30 g) to 3 oz. (90 ml ) distilled water plus a preservative. Do not heat gum arabic solution, so use it and store it away from heat and strong light. You can also use plain gum arabic around the borders before you start printing, and it will act as a mask to keep pigments and dichromate from staining that area.

I have read of a 20 percent solution of 88 percent hydrolized PVA (polyvinyl alcohol without vinyl acetate) and water being used instead of gum arabic. After letting the mixture stand for 20 minutes, it is heated to no higher than 122°F (50°C) with continuous stirring, at which point the PVA should appear clear. Any undissolved grains can be strained through a double layer of cheesecloth in a funnel. Incidentally, a form of this PVA method with ammonium dichromate is used as a photo ceramic technique on bisque ware and as an emulsion for photo silkscreen. Any user of these components should check the health hazards associated with them, and the Annotated Bibliography of this book lists appropriate organizations and books.

You will also need either potassium or ammonium bichromate, which can be purchased as a dry crystal in 1-pound (0.5 kg) or smaller bottles from suppliers listed in Supply Sources. I prefer ammonium bichromate for its greater sensitivity to ultraviolet light—it is nearly twice as fast as potassium bichromate—but using it means you have to be more careful about fogging the emulsion through accidental light exposure or letting the sensitized layer sit too long or become too hot (gum prints grow to be more sensitive the minute the coating is dried or heated).

Proper mixture, exposure, and development should avoid staining problems in the finished print, but a bath of 5 percent potassium alum and distilled water may help clear it. This bath also hardens the gum emulsion, a result especially useful with multiple coatings. Some gum printers use a 10 percent solution of potassium metabisulphite or sodium bisulfite for five minutes to clear the prints individually, as the emulsion is quite delicate and you will want to watch the action on each one and prevent one print from damaging another.

4.  Contact printing frame. On top, use plate glass that does not block ultraviolet light with Masonite underneath, another piece of glass as a backing, or follow the instructions on pages 80 for building a frame; one with a hinged back is not needed because during exposure you cannot really see when the exposure is right. However, if you are going to continue with other processes or if you are going to combine gum over other emulsions, I think you will find that investing in a good print frame will be worth it. You can find, in the Supply Sources, companies that sell them. I no longer trust pine board, foam, or foam core because they change shape after a little use.

5.  Distilled water. Sometimes tap water is fine for making the bichromate solution, but distilled water eliminates the frustration of possibly mixing bad solution. A tub filled with hot tap water can be used for warming the distilled water.

6.  Hair dryer with warm and cool settings.

7.  Household bleach (optional). Severe overexposure causes pigment stains that can be removed by adding a few drops of laundry bleach to the first water bath. You can also use this bleach and water mixture with Webril Wipes (see Philben, a lithography merchant, in Supply Sources) or cotton swabs to gently clean up borders after you finish printing. Selective areas can be lightened with a sharp typewriter eraser applied gently on a dry print. With both methods, you have to be careful not to abrade the paper.

8.  Image. Low-density (no heavy black) and low-contrast negatives the size of your intended print offer the possibility of as full a tonal range as possible (about 4–6 tones) in a single color after one exposure to gum bichromate emulsion. More often, though, the density of the negative exceeds the range of the emulsion, thus requiring multiple exposures to build up highlights, middle tones, and shadows. Posterized and color separation negatives, explained in both the Making Negatives: Digital Method, Chapter 6, and in Phil Zimmerman’s Options for Color Separations listed in the Bibliography, offer versatility, because you can create a multiplicity of colors from only three pigments. In addition, high-contrast negatives work quite well. I tried printing a low-contrast negative in alizarin crimson over a print in a dark green from a high-contrast negative of the same image. The results yielded a range of colors from deep brown to pink after just two exposures. The most trustworthy and fastest way to make a set of negatives is digitally (see pages 120–149). Remember: you have to keep inkjet negatives absolutely dry, or the negative’s image washes off. You can make color separations with a large-format camera negatives or with a pinhole camera (page 110), either with the proper filters and black-and-white sheet film or by scanning a color negative and separating it into its component colors (see Making Color Separations in Chapter 6, page 121). Even with color separations, you will find that compressing the scale (not 0 to 255, but perhaps 25 to 225 steps in the Curves Layer of Photoshop®) is about all the gum process can render. The end of this chapter shows step-by-step photos for making a full color gum print.

In addition, try stencils, found objects, torn paper, lace, and drawings on acetate. To get more than one layer of color, register negatives as described later in this chapter or in Chapter 4. Negatives made on the proper acetate (the manufacturer usually specifies what materials to use) put through a photocopy machine and photogram objects will work, too. Please look at Christian Marclay’s work on page 98 for an unusual cyanotype photogram, a method that could be used with any of the hand-coated processes.

9.  Measuring cup (4 oz. or 114 cc) and measuring spoons, clear plastic cups with white paper placed under them or shallow glass bowl or saucer, stirring rod. The small, clear-plastic 1 oz. (30 ml) medicine measuring cups available at a pharmacy are also helpful. A shallow glass bowl, such as a pudding dish found in a grocery store, or a glass saucer from the next-to-new shop, is helpful because you can place it on top of a ruler in order to measure the length of the link of pigment. And, both glass and plastic can be used atop white paper to facilitate seeing the color of the pigment more clearly. White, rather than colored, ceramics also serves the same purpose.

Avoid stirring rods that can break or chip and thoroughly wash and dry all equipment, including brushes, in water after each layer.

10.  Newspaper, paper towels, and kneaded eraser. Cover the work area with newspaper. Discard sheets as they become soiled. Blot the coating brush with paper towels. Use a kneaded eraser to pick up debris from the dried and unexposed emulsion layer.

11.  Pencil, notebook, and timer, watch, or clock. Keep copious notes with pencil on the back and outside the image area of the print. Include information about the density of the negative, type of sizing and paper, pigment color and proportions of sensitizer, and exposure method and time. In addition, I urge you to start a three-ring binder with test prints that contain the necessary data. You can also use a pencil to mark the image area before you coat the paper.

12.  Pigments. Please see the end of this chapter for detailed instructions on making a full color gum print. Professional or artist-grade watercolors or gouache in small tubes work best. Be forewarned that different manufacturers may label the same color with different names, so ask at a good art store if you cannot figure out what tube from one company is the equivalent to that color made by another company and which colors are more permanent. The quality of the pigment, as well as the color, can make a difference if you want to avoid staining on your paper. I advise students what took me some time to learn: art is what you love, so don’t scrimp by buying inferior grade supplies. Instead, save money by packing your lunch and eating dinner at home! Watercolors produce more transparent coatings and can create a variety of colors with just a few pigments, whereas gouache renders a more opaque deposit and, therefore, tends to cover the layer underneath, but gouache could be more suitable for the base or for a print that requires solely a single coating. Liquid tempera colors have been used with success, but they tend to separate into fine particles, producing a grainier look to the gum bichromate print. However, Peter Fredrick wrote about his Frederick TemperaPrint Process in Creative Sunprinting, listed in the Bibliography but difficult to find and, with Alex Chater, created step-by-step instructions on www.AlternativePhotography.com. Frederick used eggs, ammonium dichromate, and acrylic pigments. Pigments tend to be more permanent than dyes, but some colors innately last longer than others, and a good art store employee should be able to inform you about stability. I have experienced problems with Cerulean blue.

For a full-color print, I use cadmium yellow medium, thalo or ultramarine blue, and alizarin crimson or permanent rose. I do not use black but prefer Payne’s gray.

13.  Plastic clothesline and pins or drying rack that you keep clean.

14.  Protective gloves, respirator mask. In the beginning of this book, you will notice that I recommend heavy Neoprene, but Nitrile also will work with most chemicals.

15.  Registration pins, light table, masking sheets, masking tape, ½ in. (1¼ cm) heavy black tape, ruler, hole punch, scissors, stencil knife (optional). Gum bichromate printing yields subtle colors, and usually one coating with one exposure is not enough. Remember: you will probably use the negative emulsion side down so that it looks correct on top of the paper. If you are using more than one negative with multiple coatings and exposures, see Chapter 4, Creating the Photo-Printmaking Studio, which describes a tried and true registration system (see page 85) using two registration pins and a hole punch of the same diameter, whether you are using different negatives or the same one more than once. Another option that ensures image alignment when using one negative with multiple coatings and exposures requires cutting four strips of heavy black tape 1 in. (2.5 cm) long. Affix a tape strip to the center of each of the four edges of the same negative, beyond the image area. Trim the excess so that the tape is flush with the film, and with a sharp hole punch make a half-circle notch in each of the taped edges. If you coat the paper with gum bichromate emulsion beyond the image area, the hole punch method will provide a dark half-circle on every side of the print after exposure. You can line up the notches in your negative with these half-circles for subsequent exposures. In addition, at the end of this chapter, you will find directions for using push pins and cardboard for registration. A light table helps you align many negatives before you punch and arrange them.

A method that Richard Sullivan, of Bostick & Sullivan (see Supply Sources), recommends requires cutting a piece of Formica several inches larger than the paper, obtaining registration pins, Berkeley or other company registration tabs (self-sticking 1 in. square Mylar with hole punched in one end), and double-backed carpet tape. He suggests taking your paper and dry mounting it to the center of the Formica or heat-resistant plastic. Degrease one edge of the board next to the paper with isopropyl alcohol. Cut a piece of carpet tape a little larger than the registration pin and first stick it to the pin then stick the unit onto the degreased Formica next to the paper. Repeat this process with the other pin and stick it a few inches from the first pin on the degreased margin of the board. Next take each of the tabs and put them onto the registration pins with the sticky side up. Carefully attach the negative, emulsion side up, to the sticky part of the tabs. Coat the paper with the gum bichromate solution, Sullivan advises, light on pigment and underexpose it beneath the negative, which has been inserted onto the pins. Remove the negative. Process the paper still attached to the Formica, and build up layers, sizing and drying in between. When you are finished, stick the board and print in a hot dry-mount press, quickly peel up one corner of the paper, and strip it off the Formica. You can reuse the board and pins.

Tips for Making Gum Prints, below, has more detailed instructions and step-by-step illustrations.

16.  Receiver and sizing. Finished prints should be rendered on rag paper with a slightly toothy texture for the mixture to cling to, medium absorbency, and resiliency in repeated water baths, such as Fabriano Artistico Extra White Hot Press, Strathmore Artists Print paper, Arches and Lana Aquarelle 300 grams—not pounds—per square meter (gsm) watercolor block, or Lana or Cotman Watercolor pads. I am such a fan of Platine that I even use the back of it (a slightly rougher surface) because Platine is the brightest white you can find without optical brighteners, and it is both internally and externally sized the way I like. Other printers swear by Bergger Cotton 320. The backs of more textured papers (even the backs of reject prints) can be used for higher contrast work. Practice prints can be made on less expensive paper. Yupo works well with multiple coatings because it is a plastic sheet and dimensionally stable, although I am not fond of its texture.

Other surfaces that work are those with a tooth, such as the dull side of aluminum lithography plates (I “recycle” them from the printmaking department at the Museum School, where I teach), the matte side of frosted acetate, sand-blasted glass and plastic, and roughed up metals. Tyvek™, which is spun plastic that looks like rice paper, works well. It is sold at home-improvement stores as an insulating barrier against water or you can take apart a waterproof Tyvek™ envelope purchased from a stationer.

Some gum printers use white or other pigments lightened with white on dark paper. Arches Cover, Rising Stonehenge, and Rives BFK, which comes in black and dark brown, is particularly suited to this dramatic approach. Or you can brush cyanotype, palladium, or brown print solution on paper, expose it to ultraviolet light without a negative, process the paper, and get a sheet of solid deep blue or brown paper with a long exposure and a sheet of pale colored paper with a short exposure.

Sizing fills the pores of the paper so that the color stays on top, rather than sinks in, but sizing can also affect the color of the finished gum print. Unless you use the diluted acrylic polymer size by itself, all paper should be sized (see page 89) with a method that uses hot water because you will also be preshrinking the paper, an important preparation for more than one gum print coating. Otherwise, you need to preshrink paper by floating it for 20 minutes in 104°F (40°C) water, then hanging it without weighting it to dry, or drying it flat on clean screens. In an article entitled “The Gum Print,” in Darkroom Photography (Oct. 1986), James Collins suggests the following method, which I have successfully used: size the paper, then air dry it. Apply the gum bichromate emulsion to an area about 1 in. (2.5 cm) larger on all sides than the image, and hang the paper in front of a cold-air fan to dry. When the emulsion is just barely tacky to the touch, put two pencil dots 12 in. (30.5 cm) apart and about ⅛ in. (5 mm) inside the emulsion edge. Hold a hair dryer about a foot (30½ cm) from the paper (I hold it closer), and evenly blow warm air (I use hot air) over the paper until it has shrunk the paper by ⅛ in. (5 mm) and the pencil dots measure 11 in. (30.25 cm) apart. Make the exposure, develop the image, and repeat this coating and preshrinking procedure with each application of emulsion.

My personal routine is always to use a sheet larger than the image so I can take notes and register negatives outside the picture. First I use the alum and spray starch method described on page 90, then I use one layer of acrylic matte medium diluted with six parts water between each color to prevent light areas from staining. You can even tint the first layer of this diluted sizing with acrylic paint if you want a pale color to work on. You can finish a print with gloss medium over the last color to make an even more lustrous appearance than the gum arabic in the formula already provides. When I use the back of Platine, I need only use spray starch by itself; I spray and then lightly sponge brush two coats in opposite directions, letting each coat dry before I apply the next. I employ this simple procedure before each layer of color, measuring for shrinkage as described in the previous paragraph.

The other sizing methods (see pages 90) work for numerous coatings, but be aware that the highlights become tinted with pigment. With the acrylic polymer matte medium method (page 91) by mixing 1 part polymer medium with 8 parts water, you can build up more layers and keep the highlight areas bright, but the paper eventually becomes stiff. Therefore, rather than use sizing, try using white gouache, which is more opaque than watercolors, for the first coating, exposing, and processing it without a transparency. Then proceed with normal gum printing. The traditional sizing, from a time before there were plastics as found in polymer medium, is the gelatin method described on page 90.

Because sizing paper and fabric is necessary, messy, and time-consuming, you will find it more practical to size several pieces of paper or fabric at once. Keep all implements and surfaces clean and size the substrate’s side to which you will apply the emulsion. If the surface you size on is either a tray or a table, make sure it is horizontal. Using a puddle pusher, available at Photographers’ Formulary, helps ensure a flat, smooth coating.

I find that, no matter what paper or type of gum print technique I try, there is a limit to the number (for me, it is 5–6 layers) of gum-pigment-bichromate coatings that will sit on the surface. I recommend that you look at Marco Breuer’s work reproduced on page 109 of Generating Imagery: Analogue Methods for a more robust attitude about layering color.

Natural fabrics, such as cotton, canvas, and linen preshrunk (in hot water, which will also remove the manufacturer’s sizing and is counterproductive for our purposes) and surface sized, as described in Chapter 4, can be used with gum bichromate printing. I have used gessoed painters’ canvas, which eliminates the need to surface size. Practice first on paper, since imaging on cloth is a technically challenging way to work.

17.  Trays or tubs. You will need two glass, plastic, or porcelain trays larger than the print and without ridges that could damage the delicate wet gum print when you develop the image and fix it. You may also want a third tray for a stain-remover bath and a fourth tub from a grocery store for hot water to keep the bichromate solution warm so that the chemicals do not precipitate out. If you do not use protective gloves, you will need non-metallic tongs to pick up the print, and I use the wishbone-shaped plastic ones with rubber tips because they stay in one piece and last longer.

18.  Ultraviolet light and studio light. You cannot see a great color change after exposure and before development, unlike with cyanotype or Van Dyke brown printing. Artificial light such as sunlamps, photofloods, or fluorescent ultraviolet tubes (how to build an exposure unit is detailed in Chapter 4) allows the exposure to be exactly timed and is not affected by the weather, the time of year, or the time of day. A typical exposure in my studio is six minutes. However, indirect sunlight can be used; avoid direct sunlight, where bright radiant heat output can cause the emulsion to fog with exposures over five minutes.

I illuminate my studio with a 60-watt tungsten bulb 4 ft. (1.22 m) away, and I have never noticed a problem. However, in 2007 the United States Congress passed a regulation requiring new energy-efficient standards for basic light bulbs so that standard incandescent bulbs are being phased out and will no longer be produced, although standard bulbs will still be available to purchase while supplies last. A number of specialty incandescent bulbs, such as chandelier, and 65 watt incandescent flood light and ceiling fan bulbs, will remain available, and I would suggest them because some models can be screwed into a regular socket. You should run a test to make sure your paper does not fog with your studio lights on: coat and dry a sheet of paper with the emulsion, let it sit on your work table for at least 15 minutes, then develop it to see if the emulsion has been exposed or hardened. Another bulb that works is a bug light, but the problem with this light source and a traditional red darkroom safe light is that seeing the coating is more difficult. Do not be tempted to use Compact Fluorescent (CFL) or other fluorescent sources, which give off ultraviolet. In the United States, some manufacturers are already phasing CFL bulbs out and are only going to produce Light Emitting Diode (LEDs), which also emit ultraviolet. But the easiest solution of all is to do the mixing and coating—not air drying—in a room where you can cover the windows or pull the shades.

TIPS FOR MAKING THE BICHROMATE SOLUTION

You can double or triple the following recipe if you plan on doing a lot of printing, because the bichromate stock solution has an indefinite shelf life when stored in a cool, dark place. Should the crystals separate from the water, they will reblend when warmed to 90°F and stirred.

Please note: Making Negatives: Digital Method, Chapter 6, describes a method for finding DMax, or the deepest tone a process will make with solely the imageless film, which does have a light-blocking effect. You may find that different hues require different exposure times for rendering DMax.

TIPS FOR MAKING A GUM PRINT

Before you mix the gum bichromate solution, you can get a sense of how the colors will combine after you print different layers. Take a piece of paper the same color as you will be printing on and a brush, mix a dab of each color with water, and layer the liquid colors in the order you were planning to use them. Be sure to let each color dry before you add the next.

Write down every detail of your printing method so that you can be consistent when you work, because precision is not easy. After all, a 1 in. link from a small tube of watercolors will not be exactly the same as a 1 in. link from a large tube, and the density of the earth colors tends to be thicker than that of other colors, but the recipes still work. In addition, write “top” outside the image area because sometimes, after you coat a dark color, you cannot see the underlying picture.

This following, a slight departure from the method described earlier in Item 16, is a system that I find useful for making sure that after each soaking, when the rag (cloth) paper changes size, I bring the sheet back to its original dimensions so that the negatives can be registered: I make a mark on the front of the paper with a sharp pencil point at 1 in. (2.5 cm) and 8 in. (20 cm). The marks are outside the image area but within the coating area. I always use a hair dryer to dry the paper. First I use heat, and I keep re-measuring with a ruler until the pencil marks are back to their original length. Then, I change the hair dryer setting to cold.

You must thoroughly mix the pigment with the gum arabic and bichromate solution (see Step 2), or the emulsion will be streaked. Improper sizing, such as the gelatin method without a hardener, or too much pigment can cause stains in the developed printing paper. Remember, a dichromated solution will continue to lose sensitivity over time or when stored in heat or humidity, so you must use the mixed and/or coated emulsion as soon as you can.

The recipe described in Step 2 on page 214 works better for one-, two-, or three-coating prints, as it renders relatively strong shadows, good middle tones, and clear highlights (although gum prints are pale after just one exposure). An emulsion of a ½ in. link of pigment and ½ teaspoon gum arabic with 1 teaspoon bichromate solution shortens the exposure time and is better for halftone negatives, more than three coatings, and printing on fabric.

If you are going to use the same negative repeatedly, build up your image by making exposures for highlight, middle tone, and shadow areas. A good working method is to divide your gum-pigment solution into three densities:

Light: 1 in. (25 mm) link pigment to 1 teaspoon gum arabic and ½ oz bichromate solution.

Medium: 2 in. (51 mm) link of pigment to 1 teaspoon gum arabic and ½ oz bichromate solution.

Dark: 4 in. (102 mm) link of pigment to 1 teaspoon gum arabic and ½ oz bichromate solution.

Use the lightest solution for the first and longest exposure—this will give you highlights. For the middle tones, lessen the exposure by 1–2 minutes and use the medium solution. For the shadows, reduce the exposure again by 1–2 minutes and use the dark solution.

TIPS

Avoid working in extremely humid conditions, because the bichromate solution soaks up moisture from the air and becomes less sensitive and produces less contrast in the developed coating.

Make sure the polymer medium sizing is not thick or uneven when you apply it, or you can end up with large light spots after development. On the other hand, if you do not apply enough sizing, you might find that the color permanently stains the paper.

If a cap on a tube of paint sticks, you can loosen it by holding a lighted match under or running hot water over the cap for a few seconds. Clean the threads with a tissue, then apply a little petroleum jelly to the ridges to avoid this problem again. If the paint has dried up, just remove a hunk of it by cutting the bottom of the tube, then soak the dried chunks in a little distilled water until it softens. These are old art school tricks that I was reminded of by Judy Seigel.

Mix your own colors rather than depending on the manufacturer’s colors straight out of the tube.

The emulsion (see page 211) may be applied to the entire sheet of paper or only to specific areas. To make a smooth and light coating, use a foam brush and apply in quick, even strokes; for texture, use uneven strokes and a bristly brush. A foam roller can give either a pointillist effect or a very smooth surface, depending on how much pressure you exert. You can use quite a bit of “muscle” to make sure that the gum-pigment-dichromate emulsion is applied so evenly that no brush marks or air bubbles remain. However, you must work quickly or the emulsion starts drying, and you cannot move the emulsion much. Do not worry if a few hairs come off as you coat the emulsion; you can pick them off a dry print after each coating, and they will not leave a mark.

Do not apply too thick a layer of emulsion, because a heavy coating obstructs the exposure (meanwhile, a thinner coating gives better detail). A slight tooth to the paper helps prevent the solution from slipping off later, when you develop the paper but are sure you exposed long enough.

Rinse and dry your brush as soon as you finish coating the paper.

When drying the emulsion, remember that too much heat from a hair dryer will cause the bichromate to harden and become insoluble in water.

Be careful measuring the components of the emulsion because too much dichromate or too little pigment can lower the image’s contrast.

Because the emulsion becomes more sensitive to both light and heat as it dries, coated papers do not store well, and the emulsion will harden with time. Coat only as many sheets as you plan to use at one printing session. The three-part emulsion will not store well, either; so mix just enough emulsion to use, coat it immediately, and discard the rest.

You can, however, mix and indefinitely store the gum and pigment mixture without the dichromate.

Exposure times for gum printing must be determined by testing, so before you start to work on an actual print, you can reduce future frustration by running the following test: coat with emulsion and dry a sheet of paper. Cut this sheet into 2½ in. (6 cm) strips, marking each strip to indicate the emulsion used. Using a different strip but the same part of the negative, make separate exposures of different lengths of time, being sure to mark the exposure time and light source on the strip. Develop, dry, and evaluate each test for each emulsion used. Keep a notebook with these test strips for future reference, because you will notice that different colors may need different exposure times. When I use the fluorescent exposure unit described in Chapter 4, I find a 6-minute exposure to be a good starting point with “normal” negatives.

Do not worry if you cannot see a latent image on the coated paper after exposure and before development. Sometimes you can see one, but either case is not a sign of a correct or incorrect exposure.

If the image was overexposed or the light source was too hot, the emulsion will harden and will not wash off. If the image was underexposed, the emulsion will float off. If you used too thick a coating or too much pigment when applying the emulsion, the image will flake off. This problem is exacerbated with multiple coatings.

Make sure the developing tray is full of water—if the gum print scrapes the bottom of the tray, the image will rub off.

You can remove some stains by floating the print in very hot water for 5–10 minutes, but be sure to place the print in cold water immediately afterward for the final rinse. Do not be confused if you are using more than one color per coating: you should wash the yellow dichromate stain after each coating, but the highlights with detail may have yellow pigment in them, if you used that color.

If the shadows are blocked, try gently coaxing the pigment off with a soft brush in the water. Or, remake your negative with a new, flatter curve adjustment.

If you find little white bubbles on the finished print, try developing the print face-up while you watch to make sure that no run-off pools on the image.

Gum works beautifully under liquid enlargement emulsions (see Chapter 13) and over brown or platinum/palladium prints. My personal favorite is gum over cyanotype, but the dichromate in the gum tends to bleach the blue, especially with six or more coatings. Therefore, start with a slightly overexposed blueprint and size with the polymer method—which also deepens the blue print—before you coat the gum bichromate solution.

Rockland’s (Rockaloid.com) SelectaColor for paper, wood, metal, and plastics can be used in a similar way to gum printing because they are composed of a more permanent pigment base, which you coat on a receiver and expose under a contact-size negative, then sponge develop.

10.15  Graciela Olio, Casa Refugio, 25 × 20 × 20 cm (9.8 × 7.9 × 7.9 in.), porcelain (Keraflex) and gum bichromate, white stoneware, firing 1270°C, (2318°F), Oxidant, 2016. Photo Credit: Escuela de Arte de Talavera.

Created during the program of International Artistic Residencies of the School of Art of Talavera. Talavera de la Reina, Spain, Argentinian artist, Graciela Olio, grounds her work in a cultural mix of Pre-Columbian, Hispanic-American, and European ancestry. She is aware of and consciously wants to break down the traditional divide between art and craft. For more information on how to apply photo images to ceramics, see Jill Enfield’s Guide to Photographic Alternative Processes (second edition, forthcoming, 2018).

Pébéo’s Setacolor transparent fabric paints are light-sensitive when mixed with water and can be applied to either natural or synthetic fabric and used wet. You contact print objects (e.g., leaves, shells, cheesecloth) directly on top of the paints after they have been coated on cloth and put the setup in the sun or under heat lamps. When the fabric dries, you have a print without any further processing. Once the fabric is heat cured, it is wash-fast and color-fast and can be dry cleaned. Made in France, the dyes and instructions for their use also are available in the United States.

You can use the plain pigment to spot the print and lessen visible imperfections. Always start lighter than you want by adding more water to the paint.

NOTE

1  Doty, Robert, ed. Photography in America. New York: Random House, 1974.