1. List of Materials Needed for Carbon Printing

In addition to standard darkroom equipment only a few special items are needed to work the carbon process.

• Ammonium or Potassium dichromate-Used as a sensitizer.
  
• Assorted Pigments-For manufacture of pigment tissue.
  
• Carbon tissue-Carbon tissue is actually comprised of a fairly heavy paper or plastic base, coated with a rather thick layer of a gelatin-pigment mixture, with possibly some plasticizer such as sugar and/or glycerin added. It was available commercially over a very long period of time in many different colors but today we must make it. More about this later.
  
• Scale- A triple beam or one of the new electronic units measuring 0.1 g - 500g will satisfy all requirements.
  
• Densitometer-A transmission Densitometer, though not essential, can be very useful for making negatives of the correct DR for carbon printing.
  
• Distilled Water-For use in mixing carbon sensitizers and for manufacture of tissue.
  
• Glyoxal-Used as a hardening agent for sizing paper.
  
• Gelatin- Need a medium hard gelatin (175 - 300 Bloom), either porcine skin or ossein source.
  
• Glycerin-Used in tissue manufacture.
  
• Plate Glass-Several sheets of 1/4" thick plate glass, at least two inches larger on all sides than the largest prints to be made.
  
• Clear plastic- Obtain clear or white plastic of the polyvinyl family of a size at least two inches larger on all sides than the largest size print to be made.
  
• Rubber Squeegee-Should be sturdy in construction, six to twelve inches wide.
  
• Rubber Roller-This should be of hard rubber, six to twelve inches wide.
  
• Potassium Alum-Used as hardening agent for sizing the final support for the double transfer procedure.
  
• Sodium Bisulfite-Used as a clearing agent to get rid of the dichromate stain. Only needed for single transfer work.
  
• Contact printing frame-Should be sturdy construction and somewhat larger than the largest negative you plan to work with.
  
• Ultraviolet Light Source-A variety of near ultraviolet light sources are useful: the sun, a bank of BL tubes, sun-lamps, mercury vapor yard lights, and commercial light sources like the Aristo platinum printer and the Nu Arc 26-1K mercury vapor exposure system. Yellow bug lights, 15-50 Watts-These are used as safe-lights for the processing steps of carbon printing.

2. The Light Source

Sensitized carbon tissue has its maximum response in the blue, violet and near ultra-violet region at about 350-450 nanometers. It follows that any light source used for carbon printing should emit the greatest percentage of its radiation in the area of greatest sensitivity, i.e., 350-450 nm. Light sources that produce most of their radiation in the far ultraviolet give images low in contrast, whereas light sources rich in blue and green give less sensitivity but more contrast. In practice it will be found necessary to adjust the strength of the sensitizing solution to the particular light source being used.

Excellent exposure sources for carbon printing are, in ascending order of cost:

a- the sun, cheap but very unreliable

b- sun lamps, hard to find these days

c- mercury vapor street lamps

d- a bank of BL (black-light) fluorescent tubes

e- carbon arc, pulsed xenon and metal halide printers made for the graphic arts.

Each light system has its advantages and disadvantages, but when used properly all are capable of excellent results in carbon printing.

Image contrast will vary considerably with the light source in use, ranging from lowest contrast for BL tubes to highest contrast for mercury vapor, carbon arc and metal halide. However, this difference in contrast is of no practical consequence since a very wide range of contrast control can be had by varying the strength of the dichromate sensitizer.

In single transfer carbon, in which the image is developed directly on its final paper support, the final image will be reversed unless the negative is reversed during exposure. It is important to keep in mind that reversal of the negative during exposure will result in considerable loss of apparent sharpness when exposing with diffuse light sources such as fluorescent tubes. In condition where both apparent sharpness and correct image orientation are considered important it will be necessary to use the double transfer procedure when exposing with diffuse light sources.

2.1 Printing with the sun

The sun is a very powerful source of ultraviolet light but it varies greatly in intensity according to season, time of day, atmospheric condition, and geographic location. Printing should be done in the shade or in diffused light.

2.2 Sun lamps

Sun lamps are manufactured for tanning the human body. They produce quite a bit of heat and therefore must be placed at least 18-24" from the printing frame. Sun-lamps must be allowed to warm up for a couple of minutes before use, and once the lamp has been turned off it should not be turned on again for at least three minutes.

2.3 Mercury vapor street lamps

Mercury vapor lamps have a discontinuous spectrum and much of the light they produce has no effect on the sensitized carbon emulsion. Remove the plastic diffusion element from the street lamp, leaving exposed the bare bulb. Bolt the unit onto a suitable support with a reflector installed behind the bulb and connect the power line to an on-off switch. As with sun-lamps the light must be allowed to warm up for at least five minutes prior to the printing session. Mercury vapor lamps produce a lot of heat but are among the least expensive light sources available.

2.4 Bank of BL or Daylight fluorescent tubes

A bank of BL or Daylight fluorescent tubes is an excellent light source for carbon printing. Such units can be purchased ready-made from several sources or you can build your own. A fan should be added to cool the tubes because if they get hotter than about 105°F the light output decreases, resulting in longer exposure times. Fluorescent tubes do not require any appreciable warm-up time, and they may be restarted immediately.

2.5 Graphic arts printers

Graphic arts printers often come with integral vacuum frames, a very desirable feature for carbon printing. The carbon-arc, mercury vapor and pulsed-xenon light sources used in these units do not reach maximum brightness as soon as they are turned on and should be used with a light integrator, an instrument that measures the total amount of light available for exposure.


3. Negatives for Carbon Printing

3.1 In-camera negatives

The best negatives for carbon are made in the camera, exposed and developed to maximize the very long scale inherent in the process. Such negatives are, in the language of photographic literature of the past, stout, appearing on inspection to be somewhat over exposed and overdeveloped. For best results and expose and develop for a density range of about 1.6. Negatives which print well on a grade #0 or #1 silver paper should also print well in carbon.

3.2 Enlarged negatives

Excellent carbon prints can be made from enlarged negatives if good working procedures are followed. Enlarged negatives can be made in the following ways:

In making enlarged negatives it is very important to consider the desired orientation of the final print. Expose the original in the enlarger in such a way that the final negative to be used in carbon printing can be used with the emulsion of the negative facing the emulsion of the tissue.

3.2.1 One-Step Direct Negative Method

This is the easiest way to make an enlarged negative for carbon printing. An enlargement is made from the original negative on Kodak Direct Duplicating Film which, when developed in ordinary chemicals, gives a negative. For proper image orientation of the final print; place the original negative in the enlarger emulsion side down for single transfer work, emulsion side up for double transfer.

3.2.2 Enlarged Negatives by Reversal

It is also possible to make enlarged negatives in one step with Kodak T-Max 100 film and Kodak's special reversal processing chemistry. Due to the speed of T-Max, exposures in the enlarger will be very short, and the use of either a digital timer or neutral density filter will likely be necessary. There is virtually no exposure latitude with this process, so it is vital to make careful exposure tests. To minimize fogging of the negative, cover the easel with a black sheet of paper and make sure there is no light leaking from the enlarger. The reversal chemistry increases contrast, so when working with negatives made for silver printing follow Kodak's recommended procedures for normal development, and the increase in contrast should give a suitable negative for carbon work. Another excellent method for making enlarged negatives by reversal is described in an article by Liam Lawless in Issue # 2 of The World Journal of Post-Factory Photography. This method is based on the use of Freestyle APH or APHS lith film and a special bleaching chemistry.

3.2.3 One-Step Direct Negative from a Slide

A negative for contact printing can be obtained by enlarging a color transparency directly onto a sheet of film of the size desired for the final print. Because color transparencies already have high contrast and density the resulting negative should give excellent results in carbon printing. Orient the slide according to your working procedures: for single transfer, the transparency should be placed in the enlarger emulsion side up; for double transfer work, emulsion side down.

3.2.4 Two-Step Positive-Negative Procedure

When starting with an original negative of small size, two approaches are possible:
1) by enlargement make an inter-positive of the size required, and use the inter-positive to contact print the final negative; or
2) make an inter-positive by contact printing, and use it in the enlarger to make the negative. This procedure allows for more control of the density and contrast of the final negative because corrections can be made to either the inter-positive or final negative. The original negative should be placed in the enlarger emulsion side down (or contact-printed emulsion to emulsion) for single transfer work, emulsion side up for double transfer. See John Rudiak's excellent article on making enlarged negatives in Coming into Focus.

3.3 Paper negatives for carbon printing

The final negative can also be made on a bromide paper instead of film. This was a very popular technique of pictorialists during the first decades of the 20th century and is capable of very interesting results. The Spanish pictorialist José Ortiz-Echagüe printed his Fresson prints exclusively from paper negatives. There are some disadvantages to the use of paper negatives. Image sharpness will be degraded, though not so much as one might imagine, especially if a thin bromide paper is used. To minimize the appearance of paper texture pre-flash the paper briefly from the back before exposure. Determination of the exact exposure needed to achieve this will take some experimentation, but for a starting point, try the following:
1) adjust the enlarger lens so that a reading with your light meter off a piece of white paper under the light indicates an EV of approximately 2.5;
2) place the paper face down on a piece of black paper; and 3) expose for 6-10 seconds. A disadvantage of paper negatives in carbon printing is the very long exposure times they require. Paper negatives on single-weight fiber papers will have a base-plus-fog value of about 0.8, higher if pre-flashed. This results in very long exposures.

3.4 Digital negatives for carbon printing

The use of digital negatives is becoming increasingly popular among practitioners of many of the alternative photographic processes. An image is scanned and the information placed in the computer, then using Adobe's PhotoShop or other image editing software it is manipulated to increase apparent sharpness, change local or overall contrast, correct local imperfections, etc. When printed at high resolution by a service bureau digital negatives are capable of outstanding results in carbon printing. There are a number of good sources on making digital negatives, the best know of which is probably Dan Burkholder's book on the subject. See also the chapter on making digital negatives for alternatives processes by Charles H. Palmer in Coming into Focus.


4. Manufacture of Materials

4.1 Carbon Tissue

Photographers interested in working the carbon process in monochrome must learn to make carbon tissue and the various paper supports because there are no commercial materials available at this time. The home-manufacture of these materials can be quite time-consuming, especially in the learning stages, but it is not extraordinarily complicated, and with a little experience very satisfactory carbon tissue can be made.

4.1.1 First a word about gelatins

Gelatin is extracted from many sources, including the hides, skin, white connective tissue, and bones of animals. Its usefulness in carbon/carbro photography is due to the following attributes: it absorbs water and swells with increased temperatures until it reaches a melting point, at which point it forms a colloid; when again cooled this colloid will set, even at low concentrations, and the cycle can be repeated. As a practical matter the carbon/carbro printer need not be overly concerned with the manner in which the gelatin is derived. Most commercially available gelatins work reasonably well with both carbon, and good results are possible with a variety of materials, ranging in Bloom from 100 to over 250, including Knox food gelatin. The principles involved in the use of gelatin as they apply to the carbon process are as follows: gelatin, when added to cool water, will gradually absorb water over a period of 30-60 minutes, as its molecular structure permits; in general the higher the Bloom index of the gelatin, the more water it can absorb. This is one of the reasons published formulas for making carbon tissue specify gelatin solutions ranging from 7-15%. You will discover that increasing or decreasing the gelatin percent solution will change the setting time (time it takes to harden) of the coating solution: lower percent solutions take longer to set, while high percent solutions set much faster.

The quantity of pigment needed to coat a carbon tissue of a specific size depends not only on the opacity of the pigment, but also the amount of coating solution used. Carbon tissue can be made in virtually any color imaginable.

4.1.2 Steps for the manufacture of carbon tissue

1- Start with 900 ml of distilled water in a wide-mouth glass or plastic container, at about 70° (21C). Stir 100 grams of 175 Bloom gelatin into the distilled water, and let the mixture stand for at least one hour.

2- After one hour, place the container of the above mixture in warm water at around 110-120° (43-49C) and allow the solution to completely liquefy.

3- Remove the container of gelatin solution from the warm water, stir in about 25 grams of plain white sugar, and allow to dissolve completely.

4- Mix in the pigment. For a warm black tone tissue of normal contrast use about 40g liquid Sumi Ink. The amount of pigment added to the gelatin solution affects tissue contrast: a low contrast tissue is made by using enough pigment to produce a tissue coating that is just barely opaque. Adding more pigment to the solution results in higher contrast tissue. Low contrast tissues produce images with greater relief because the exposing light can penetrate very deep into the coating. Tissues which have been coated with a great excess of pigment produce high contrast images low in relief, because they allow only limited penetration of the exposing light into the tissue. Tube water-color pigments and other pigments in aqueous dispersion form may also be used but will require more effort to disperse thoroughly in the gelatin solution.

5- Place the container of gelatin-pigment solution in water at about 110-120° (43-49C) and leave for about an hour. During this time most of the air bubbles caused by the vigorous stirring will disappear, and the pigment will be more thoroughly dispersed.

6- The final step in tissue manufacture is to coat a suitable paper or plastic base with the gelatin-pigment solution. Many of the smooth drawing papers make good carriers but are relatively expensive to use. It is not important that the carrier have archival qualities for it will be discarded after use. A very good and inexpensive paper carrier is white poster board of the 22X28" size, though some brands will delaminate in hot water. Another good support is plain white wallpaper. In the plastic area, Denril Multi-Media Velum and some types of Mylar also work well.

4.1.3 Coating the tissue

For the coating operation the room temperature should be at about 70° (21C). The gelatin-pigment solution should be at about 100-110° (38-43C) when poured onto the carrier.

Maintain the temperature of the coating solution at a constant level throughout the operation. Do not wear wool or other clothing that has a tendency to shed lint particles while coating.

Begin preparation for coating operation by first leveling a piece of plate glass several inches larger on all sides than the largest tissue you intend to coat and placing the paper or plastic carrier in a tray of warm water.

Next, place the wet paper or plastic carrier on the leveled glass, squeegee off all surface water and blot off with a clean towel. Very slowly, and without creating any air bubbles, the required quantity of gelatin-pigment solution into a small glass or plastic measurer (20 ml for a 5X7" (15X18cm) tissue, 55 ml. for an 8X10" (20X25cm), 100 ml for a 11X14" (28X36cm), and 205 ml for a 16X20" (40X50cm). The pigmented gelatin solution should be free of any foam and bubbles.

With a gentle motion, carefully pour the solution onto the center of the carrier. Working quickly spread this mixture evenly on the carrier with your fingers. After you have finished smoothing out the coating, look over the surface carefully and remove air-bubbles and any lint, hair, or other foreign particles that may have settled on the gelatin during the coating operation.

The coating mixture should harden in ten minutes or less at a temperature of around 70° (21C). The pigmented gelatin should not flow over the edge of the paper or plastic carrier; if it does so consistently you should either increase the percentage of gelatin in the coating solution, or lower the temperature of the coating room.

Once the gelatin has set, carefully transfer the newly coated tissue to a drying screen and set aside to dry. Drying will take from 15-24 hours, depending on temperature and humidity, and may be accelerated by the use of a fan.

4.2 Final Support for Single Transfer

In single transfer the carbon image is developed in warm water on its final support, which may be either a fixed-out sheet of photographic paper, or a watercolor paper, which has been sized with a layer of gelatin.

The procedures for preparing these supports are as follows: Photographic Paper, Any good quality photographic paper, may be used as the final support in carbon depending on the desired surface. The appearance of detail will of course be greater when the final image is on a smooth, glossy surface paper. However, luster and matte surface photographic papers are also good for retaining apparent sharpness. Matte surface papers accentuate the relief characteristics of carbon prints and make excellent final supports.

For use in the carbon process as a final support photographic papers must first be placed in a fixing bath for 5-10 minutes, washed thoroughly, and allowed to dry.

Watercolor Paper Medium weight, hot-press paper with a smooth surface make excellent final supports for carbon work. Cold-press papers may also be used but they have very textured surfaces which will tend to diminish the apparent sharpness of the image.

The paper is first sized with a gelatin coating, and this must in turn be hardened.

The gelatin coating is applied by soaking a sponge or brush in a warm gelatin solution and brushing it directly on the paper. Depending on the paper it may be necessary to re-coat at least one additional time.

Steps in coating final support papers are:

1- Prepare 1000 ml of a 2-3% gelatin solution. First soak the gelatin in cold water for about an hour, then place it in a water-bath, gradually raising the temperature to about 110-120° (43-49C). Then add about 10ml of a 40% Formalin or Glyoxal solution to the warm gelatin.

2- Soak the paper in warm water, then place it on a piece of leveled plate glass and use a rubber roller and clean towel to remove the excess water.

3- For a 22X30" (56X72cm) sheet of watercolor paper use about 100 ml of the warm gelatin solution, spreading it on the paper with a clean foam brush. For different size papers adjust the ratio accordingly.

4- When the gelatin sets, hang the paper to dry.

Make smaller or larger quantities of the coating solution as required. 1000 ml is enough to coat about 10 sheets of water color paper of 22X30" size.

4.2.1 Final Appearance of Image

The nature of the sizing is one of the factors that determines the final appearance of the carbon print. As a general rule the more gelatin one uses to size the paper, the smoother will be its surface, and the glossier the final image.

If the final print is too glossy for your taste, prepare a 10% corn starch solution and add about 50ml of this to the warm gelatin solution. This will give a more matte appearance.

Carbon prints on well-prepared watercolor papers offer the ultimate in permanence, with archival qualities superior to all other photographic processes, including platinum.