An excerpt from Steve Anchell’s book – The Darkroom Cookbook on Printing-Out Processes.
“You must always believe that there is fertile soil for your ideas. If you lose hope then you will miss opportunities to plant a seed.”
The term “printing out paper” and the associated initials P.O.P. were introduced in 1891 by the Ilford Company for their gelatin-chloride papers. The term has since been applied to any paper that requires ultra violet light to form a complete image.
The use of printing out papers is a time-honored method for making inexpensive prints without a darkroom. Indeed, prior to the 1880s, these papers were the most popular method for obtaining photographic prints. The printing technique is simple: the paper is contact-printed with a negative using the sun for a light source to make a visible image without development (a UV lamp, available from grocery and hardware stores, can also be used).
There are several different printing out papers including salted paper, albumen, gelatino-chloride and collodio-chloride, differing in the medium used to suspend the light-sensitive substance and if the sensitizer is applied in the salting solution (as in an emulsion) or as a second step. In salted paper the silver is held by the fibers of the paper while albumen papers use egg whites as the binder. Gelatino-chloride papers suspend the silver in a gelatin layer and collodio-chloride use a binder of cellulose nitrate.
The basic light-sensitive substance used in all of these papers is silver chloride with an excess of silver nitrate. Once the image has been printed and toned, the rest of the procedure is like handling a silver print. It is fixed, washed, dried, and preserved in much the same way.
Because the silver particles of printed out images are a much finer size than those of developed out prints, they are more susceptible to deterioration. But with proper processing they will stand the test of time as well as the originals. Collodio-chloride is actually the most stable silver printing process because the nitrocellulose binder hermetically seals the silver from the harmful atmosphere that fades all silver base photographic prints.
Printing out papers can only be contact-printed. For this reason a 4 x 5″ or larger negative is usually preferred. A good print for these papers requires a dense negative with good shadow detail and clear base in the deepest shadows. Printing out papers rely on a technique called self-masking. This means that thin areas of the negative allow the light to quickly darken the paper and block light from reaching the lower layers of the sensitive surface. The result is that the shadow areas are held back slightly allowing the highlights of the picture to print.
Making a simple silver chloride salt print begins with the selection and preparation of the paper. Arches Hot Press Watercolor and Crane’s Kid Finish AS 8111 are two good choices.
Experiment with any good quality 100% cotton paper.
Before proceeding, identify the front of the paper. This is important as fine papers are made to be used only on one side. Once the paper has been prepared, it is often harder to identify the front. If the paper is in a tablet or pad, the top side is the front. If it is purchased as an individual sheet, the easiest way to identify the front is to hold it up to the light and look for the watermark.
If the watermark reads correctly, left to right, the paper is oriented to the front. If there is no watermark, the front surface is often smoother and brighter. Finally, a factory-deckled edge always bevels up to the front surface. Having identified the front, place a mark on the back with a pencil. Many experienced printers like to use paper one size larger than the negative. For example, with an 8 x 10″ negative they may use a 9 x 12″ or 11 x 14″ piece of paper.
Salting the paper
The next step is to coat the paper with a gelatin or starch salting emulsion, a process known as “sizing.” The salting formula not only prepares the paper to receive the silver nitrate but also creates a finish that keeps the image from forming deep into the fibers of the paper. Salt prints are made with either sodium chloride or ammonium chloride. The choice of a particular salt is one of the creative controls you have over the look and feel of your final image.
Salting formulas with gelatin will produce cooler prints than those using starch. The paper may be floated upon or immersed in the salting solution for 2 to 3 minutes, or it may be coated by means of a brush then hung to dry. The floating and immersion methods use more solution, but it is easier to obtain an even coat. Brush coated papers can be dried with a hair dryer, floated or immersed papers are usually dried by hanging on a line using plastic clothes pins.
Sensitizing the paper
After the paper is salted and dried, you will need to sensitize it before printing. Sensitizing may be done by tungsten light, though a bright Kodak OC safelight is preferable. As with salting, the paper may be coated by floating or with a brush then hung to dry. Do not immerse the paper in silver nitrate! If a brush is used, sensitizing should be done first lengthwise, then across, to distribute the solution evenly.
The paper, having been coated, is now light-sensitive. It can be dried with a hair dryer on the cool setting under a safelight or left to dry in a dark room. If you live in a humid area the paper should be used immediately after the silver coating is dry to prevent it from discoloring. Adding drops of glacial acetic acid to the silver solution to lower the pH to around 3.5 will slow down the tendency of the paper to discolor.
Caution: Silver nitrate stains skin and clothing. Wear rubber gloves. Should staining result, try removal with one of the stain removers under Formulas: Miscellaneous.
Coating the paper
Cover a large flat board with a sheet of blotting paper. Good quality 3/4″ plywood or an old bread board is perfect for this. Tape the perimeter of the blotting paper onto the edges of the board. To make the process of brush coating easier, buy a cheap plastic Lazy Susan to place under the coating board. This will allow turning the paper at right angles quickly and easily for brushing the solutions onto the paper from different orientations.
Brushing the solutions
The usual technique for brush-coating the paper is to make tick marks with a pencil at the corners where the negative will be positioned. Tape or pin the corners of the paper to abe coated onto the coating board. Then, using a good quality artist brush (an inexpensive foam brush works well, but soaks up a lot of solution), coat the salting solution and sensitizer over a slightly larger area in overlapping rows. After coating the paper, quickly turn the coating board 90 degrees and brush the paper again without adding any more solution. Turn the board one more time and brush again. The second and third brushing is to aid in distributing the solution evenly on the surface of the paper.
Brushing on the solutions is a critical part of the process and the one that gives printers the most difficulty. The problem is compounded because the sizings and salt water are clear and can’t be seen while they’re being applied.
NOTE: An alternative to coating with a brush is to use a glass coating rod, such as those available from Photographers’ Formulary and Bostick and Sullivan (Resources). This is a method used by many platinum printers to obtain a smooth, even coat.
Floating the paper
Coating paper by floating was the most common technique of the 19th century. The solutions, either salt or silver nitrate, were poured into a glass dish larger than the paper to be coated. For prints 8 x 10″ and smaller, Pyrex® baking dishes are perfect for this application.
Plastic trays with flat bottoms are good, but more difficult to clean thoroughly. There are two ways to prepare the paper for floating; folding two opposite corners to create small tabs or folding a 3/4″ flap along two opposite ends of the paper.
Holding the paper by the corners or the end flaps, allow the paper to sag in the middle. The middle is lowered until it makes contact with the solution and then the sides are lowered until the entire piece of paper is floating. Keep the solutions from flowing to the back of the paper. If the paper starts to curl, hold the flaps with your finger tips and breathe onto the back of the paper.
Increasing the humidity with your breath will relax the paper. Float the paper on the salting and silver solutions between 1-2 minutes. Hang on a line using plastic clothes pins to dry.
Printing out papers are printed using a wooden contact-printing frame with a hinged back or between a piece of glass and a flat plywood board of the same size. If the paper is not thoroughly dry, it can cause stains on the negative. If you’re concerned about damage to your negative or are using an historic negative, place a thin piece of clear acetate, available at art stores, between it and the paper.
When exposed to the light source (sunlamp or sunlight), the paper will darken quickly at first and then slow down. When using a contact-printing frame, you can check the progress of the print by taking the printing frame away from the primary light source in a darkened room and unhinging the long side of the back. Peel back the edge of the print to inspect the progress. Be careful not to fog the paper by exposure to bright light or to move the registration. The highlights should be darker than the tone desired in the final print, and the shadows may even have a metallic sheen called bronzing. With practice you’ll learn to judge when the print has reached the proper density.
Four techniques can be used to control the contrast of the print.
- Printing can be done slowly in the shade on a sunny day or by artificial light.
- A piece of tracing paper can be placed on top of the glass to slow down the printing in the shade or under artificial light.
- The sensitized paper can be fumed with ammonia.
- Potassium dichromate can be added to the salting solution.
Chemical Control of Contrast
Fuming the paper with ammonia changes the pH of the silver halide to an alkaline state. This technique was used in the 19th century with all printing out papers. Buy a large plastic storage box and line the bottom with cotton wool. Drizzle three ounces of household ammonia evenly over the cotton and close the lid. Do not breathe the fumes when opening the lid. To fume, tape the paper sensitive side down to the underside of the lid by four corners and replace the lid. Fume for about 1-3 minutes. Remove the paper and allow to out-gas for about two minutes before placing in the printing frame. Fuming is very effective. The paper will print much faster and will have more contrast.
Controlling contrast by light
Further control can be gained through the choice of light source. The slower the printing, the higher the contrast. The higher the amount of ultraviolet (UV) light, the lower the contrast.
Sunlamps and direct sunlight both contain relatively high amounts of UV and give the lowest contrast. However, by placing one or more sheets of tracing paper or a sheet of frosted glass over the printing frame contrast will be increased dramatically. The printing frame may also be placed on the shaded side of a building on a sunny day for a similar effect.
Processing the print
The print should first be washed to remove any free silver nitrate. Free silver nitrate will precipitate gold from the toning bath and interfere with fixing. This step is done using tap water that contains chlorine to precipitate the excess silver. If your tap water does not contain chlorine add a pinch of table salt to the wash water. Wash until all milkiness in the water has been removed. Using a dark tray or placing a sheet of black Plexiglas® in the bottom of the tray makes seeing this precipitate easier. At this point the paper has lost most of its sensitivity, but it is still sensitive until fixed.
Without toning, the final print will tend towards a warm brown color. Toning is done after the first washing step and before the fixing bath.
By toning with gold you can create a variety of colors ranging from reddish brown to purple to blue-gray. Toning also increases the permanence of the print, not unlike silver-gelatin papers.
As a rule, acid toners, such as P.O.P. Borax Toning Bath, act slowly and tend to be warm; alkaline toners, such as P.O.P. Thiocyanate Toning Bath, act more quickly and tend to be cool, or blue. If gold toning is intended, trim the darkened edges from around the print so that you don’t waste gold solution.
It is difficult to judge the final tone of these papers as the color gets cooler as they dry. It is a good idea to print out several step tablets and place them in the toner at 3-minute intervals.
Carefully mark each one and keep them for reference.
After toning fix the print in fixer without hardener for about five minutes. After fixing, immerse the print in Hypo Clearing Agent (HCA) and wash as you would any double-weight, fiber-base paper.
Other Printing-Out Processes
That’s all there is to making simple salted paper prints. The processing of salt prints is identical to the other printing out papers, so if you know one type you have a basic understanding of the whole family. Alternative printing processes, such as albumen, salt, gum, gelatin-chloride, collodio-chloride, platinum/palladium, carbro, and others, can be rewarding avenues of creativity. The level of difficulty is minimal when measured against the great control and freedom of expression available through manipulation of the process.
Scully & Osterman on gold toning
by France Scully Osterman and Mark Osterman
Most people don’t understand how much the depth of printing establishes the final image tone and are confused when they get wimpy tones from a toning formula. This is usually the case when their negatives don’t have enough density or spectral density and fogged base.
This bicarbonate type toner gives warm red brown to cool brown to purple brown tonality depending on the depth of printing and depth of toning. It can be used immediately after mixing.
The formula is based on the 19th century method of adding gold by the grain to the water in a formula, though it has been altered to use the method of percent solutions. This is because percent solutions were not used in the 19th century. The standard for making and using a gold chloride percent solution is to dissolve one gram of gold chloride into a given quantity of water as follows:
Gold Chloride Stock Solution
- Gold chloride, 1.0 g
- Distilled water 154.0 ml
Based on the above example, every 10 ml will give you one grain of gold. So when a vintage formula calls for “X” quantity of water + so many grains of gold + the pH modifier it’s easy to formulate.
Gold-Bicarbonate Toning Formula for Albumen, Salt, and Collodion Paper
- Gold, 20 ml of the stock solution given above
- Distilled water, 700.0 ml
Bi-carbonate of soda to test pH 8
More water or more gold can be added to make the bath more controllable if needed. For toning salt prints (which tone much faster) we start with 1 gram gold and tweak as needed.
Sel d’Or (gold with hypo) One Step Fix/Tone for Salt and Albumen
We usually mix this formula “to taste” but essentially it’s about four to six grains of gold stock solution in a mixture of 1000 ml with 150 grams hypo and a pinch of bicarbonate. The print will initially lighten up when first applied, but then darken gradually as gold replaces the silver.
Like all toners, it’s more effective if this action is slow… tweak the gold content to require about five to ten minutes rather than less time. This was the very first toning approach for photographic prints and was taken directly from the technique used to gild daguerreotypes except that in that technique heat was applied to the underside of the plate during the process.
Collodio-Chloride Printing Out Paper
also known as Collodion Aristotype Paper by Mark Osterman, Process Historian, Advanced Residency Program in Photograph Conservation, George Eastman House, International Museum of Photography, Rochester, NY
© 2008 Mark Osterman. All rights reserved. Reproduced by permission of the author.
The use of collodion for emulsion processes was first suggested by Marc Gaudin as early as 1861, but his efforts never went further than the experimental stage. Collodion chloride emulsion papers were made commercially by G. Wharton Simpson by 1865, but the papers were not universally accepted until the1880s when clay coated paper stock was adopted for photography. In 1884 Liesegang introduced a collodion chloride emulsion for paper which he called Aristotype, a name that is associated with both gelatin and collodion chloride papers manufactured by the Aristotype Company in Jamestown, New York.
The Aristotype Company in Jamestown, New York, introduced the most popular collodion papers in two different finishes: glossy and matte. The formula below is for making a glossy finish paper. Glossy papers were typically toned to a purple brown using gold chloride. Matte papers were toned with platinum and gold and look very much like a platinum print. Regardless of the finish or toning approach, collodion papers were the most archival of all silver halide photographic papers and are easily identified today because they are usually found in excellent condition.
Caution: Collodion, the binder for this emulsion, is a clear viscous solution made by dissolving nitrated cellulose in ether and alcohol. It is flammable and you should take care not to coat papers or expose open containers of collodion to the presence of sparks or flames.
Formulae and emulsion mixing directions
The alcohol listed in this formula is ethyl alcohol (also known as ethanol or grain alcohol).
The strength should be as strong as possible since water will be used to dissolve some of the solid chemicals. Some water is necessary in collodion formulas, but too much will cause chambered markings in the film called “crepe lines.”
The following can be done under common household light.
- Strontium Chloride, 1.0 g
- Alcohol, 4.0 ml
- Glycerin, 4.0 ml
- Distilled water, 5.0 ml
Add the strontium chloride to distilled water and dissolve by gentle heat and agitation using a glass rod. Add to this the alcohol and glycerin and mix well.
- Collodion USP, 250.0 ml
- Alcohol, 85 ml
Add the alcohol to the collodion and mix until dissolved. Add chloride Solution A to the collodion Solution B and mix well. This is now called “Salted Collodion.”
- Citric acid, 1.8 g
- Alcohol, 2.0 ml
Add the citric acid to the alcohol and mix until dissolved. Add this to the Salted Collodion Solution.
- Silver Nitrate, 6.0 g
- Distilled Water, 7.0 ml
- Alcohol, 20.0 ml
Add the silver nitrate to some of the distilled water and dissolve. The less water you use to dissolve the silver the better. Add the alcohol to the silver solution and mix until dissolved.
You will now have two distinct solutions; the Salted Collodion and the Silver Nitrate. The emulsion is made by carefully combining these two solutions.
Making the emulsion
A mechanical magnetic stirrer is great for emulsion making. In lieu of that, you may stir the solution with a glass rod in one hand while adding the silver solution with the other. The following should be performed under safelight conditions, using either amber or red light.
Making an emulsion, either gelatin or collodion, involves adding silver nitrate solution in a controlled manner to the halide solution with constant agitation. The silver may be added by using a plastic hypodermic syringe with a fine opening. In collodion emulsions the silver may be added in a thin continuous spray while the collodion solution is being stirred. As the silver is added the collodion will change from a clear liquid to an opalescent color.
Once the silver is added, pour the emulsion into a very dark brown glass bottle, or better yet search your local antique shop for the less common black glass bottle. Cork the bottle and shake it vigorously for a couple of minutes. Set the bottle aside, undisturbed for at least a day. Never allow the emulsion to be shaken again, as this will stir up any precipitates and produce millions of fine bubbles, both of which will make it impossible to make an even coating. The mixed emulsion has a remarkable shelf life if kept in a cool dark place.
Coating Paper with Collodio-Chloride Emulsion for the printing-out process
Because collodio-chloride emulsions are alcohol/ether based, paper for coating must be either heavily sized with hardened gelatin or coated with a baryta layer. The baryta layer (as used in all commercial gelatin based photographic papers) contains an inert white solid suspended in hardened gelatin. Baryta coated papers are becoming more difficult to find as traditional silver-based photographic papers fall from the marketplace. If uncoated papers are used, the solvents in the collodion emulsion will flow right through the paper fibers.
Cut a sheet of glass an inch larger on all sides than the paper you wish to coat. De-sharpen all the edges with a sharpening stone to prevent accidental cuts. Fold up a 1/2″margin on all the edges of your paper and carefully secure the paper onto the glass sheet using small pieces of masking tape.
If you already do the wet collodion process, the following technique is the same for coating plates. Holding the glass supporting the paper in one hand, pour the collodion emulsion onto the center of the paper. Tilt the paper so that the emulsion flows to all the corners covering the entire sheet. Pour off the excess emulsion from one corner back into the bottle. This draining step may result in diagonal lines forming in the surface of the coating. To prevent these, rock the plate from side to side during the draining step. Keep the corner from which the collodion was drained lower than the rest until the collodion starts to set to a firm gel.
Once the collodion has set, carefully detach the paper and pin it up by one corner to dry in a darkened room. Because collodion emulsions are solvent based, the emulsion will dry to a hard film in minutes. Once coated, it can be printed immediately or preserved for days in a light tight box. Collodion printing out paper is toned and processed using the same technique as described in the salt printing directions.
The only difference between collodion coated papers and all the others is that during processing the paper may curl slightly. This is because the collodion side will not easily absorb the processing solutions. This effect can be corrected by using solutions slightly warmed or a smaller quantity of solutions in each tray.