A dash of salt

A description of the salted paper print process with some interesting variations by Wynn White.

Always be careful when handling chemicals. Read the health and safety instructions.

Writer and Photography / Wynn White

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Combine hydrochloric acid and sodium hydroxide and what do you get? That’s right, sodium chloride commonly known as table salt. Salt is one of two key ingredients in the making of salted paper prints.

The salted paper process was invented by William Henry Fox Talbot, known as The Father of Modern Photography, in 1833 while he was on his honey moon. He was the first to make a silver image on paper. On his first attempts paper coated with a silver nitrate solution and exposed to light only gave a faint metallic silver image. He later discovered that by first applying salt to the paper and then coating it with the silver nitrate solution he could get a much stronger image. This is basically the same way that we make salt prints today.

Salted paper printing process

Recipe I: Table Salt

• Sodium Chloride 2.0 gm
• Distilled Water to make 100.0 ml
• Silver Nitrate 12.0 gm
• Distilled Water to make 100.0 ml

I recommend starting with this recipe since it is the most basic. The amount of salt can be altered slightly but at three grams per 100 ml the paper prints a very faint violet unless double coated with silver. At four grams per 100 ml I could only get a faint violet image. It is possible to make prints with much lower salt concentrations than the standard 2%. Substituting ammonium chloride for sodium chloride moves the print color from sepia towards more of a reddish brown and also increases print speed slightly. The amount of silver nitrate solution can be lowered to around 10% (10 grams per 100 ml).

Method

1Mix up the salting solution. Before coating write the name of the paper on the back in pencil for future reference and also so that after it is coated and dried you will be able to tell which side the coating is on. Smooth, preferably hot press, paper works best. It is important that the paper not be too porous since the solutions will have a tendency to sink in too deeply. One paper that I have found to work nicely with no additional sizing is Rising Stonehenge. Using masking tape, tape the paper at the corners to a heavy sheet of glass. Measure out an appropriate amount of salting solution. I use a pipette that I have marked so that the amount of solution won’t vary from print to print. Coat the paper. I like to use a glass rod for coating.

A detailed description of glass rod coating can be found at Bostick & Sullivan. http://www.bostick-sullivan.com/newbook/Page_thumbs.htm.

Use a foam brush or hake (Japanese generic term for brush) if you want prints with painterly brush marks. Allow the paper to dry. A hair drier at any setting can be used to speed up the process. Salting can be carried out under bright light and the salted paper will keep indefinitely.

2After the salted paper is dry, under safelight conditions, coat it with the silver nitrate solution. Salted paper is mainly sensitive to ultraviolet light so exposure to low level tungsten light will not fog it. Just to make sure that my paper doesn’t get fogged I work under the light of a 7 watt, yellow light bulb placed one meter above my coating area and another one above my darkroom sink. Be very careful not to get silver nitrate on your skin or, more importantly, in your eyes. It could blind you. If you use brushes you should use a separate brush for each of the two solutions. I use two separate pipettes and coating rods.

3Dry the paper in the dark. If you use a hair dryer use the cool setting. The paper is now ready for printing and should be used right away to avoid fogging.

Recipe II: Tokyo Bay Water

• Tokyo Bay water: 50.0 ml
• Distilled water to make 100.0 ml
• Silver Nitrate 12.0 gm
• Distilled water to make 100.0 ml

I collected the bay water in a Suntory whisky bottle that had washed up on the beach. When I got home I boiled it to kill the plankton. Coating and drying are the same as in Recipe I. The problem with using sea water is that it is difficult to judge how much salt there is in the water. One method of testing for salinity calls for silver nitrate, one of the main ingredients of the salt print.

I learned that there is, on average, 35 grams of salt in a liter of sea water and slightly less in bay water due to fresh water runoff. I mistakenly calculated that it was a 30~35% solution and mixed my first salting solution one part bay water to fifteen parts distilled water. Even with this small amount of salt I was able to get a nice print that was quite pink in color. After realizing my mistake I made another salting solution mixing it one to one and got a sepia colored print.

Image above: Rocksurf (Tokyo Bay Water print).

Note: If you absoulutely have to try this variation but don’t have access to Tokoy bay water, Wynn will be happy to send you some, just send him the postage… 😉

Recipe III: Wynn’s Favorite

Salting Solution

• Sodium Chloride 2.0 gm
• Potassium Citrate 2.0 gm
• Distilled Water to make 100 ml

Mix the salting solution and coat the paper. I use a coating rod.

Silver Solution

• Silver Nitrate 12.0 gm
• Distilled Water to make 50.0 ml

Citric Acid Solution

• Citric Acid 6.0 gm
• Distilled water to make 50.0 ml

Just before coating combine equal parts of the silver solution and citric acid solution. Coat the dry, salted paper with the silver nitrate/citric acid solution. If the citric acid is added to the silver solution and then stored, after time, an unwanted precipitate will form. The citric acid helps prevent fog.

Sodium chloride is used in this recipe but ammonium chloride gives results that are almost the same. The amount of potassium citrate can be lowered or omitted and sodium citrate can also be used in its place. Citrates seem to give deeper richer browns.

I mask off my prints to give a neat border around the image area. With the basic salt recipe I kept getting slight to moderate fog in the masked area. After adding citric acid to the silver nitrate solution the fog went away. I strongly advise masking, at least in the beginning, so that you can see whether or not your prints are clearing properly.

Contrast Control

The safest and most natural way to gain contrast if you are using a UV printer is to use sunlight. The boost in contrast is substantial.

A very efficient but more dangerous method of contrast control utilizes potassium dichromate. Before using this chemical you should be familiar with its hazards. An MSDS for potassium dichromate can be found at https://www.fishersci.com/msds?productName=AC197760050.

A general rule would be never to let it come in contact with any part of your body or to breath in any potassium dichromate dust, even in minute quantities.

I have mixed solutions of potassium dichromate from.5% to 10% and keep them in separately numbered bottles; each bottle being successively.5% more concentrated. Before coating I add one drop of an appropriate potassium dichromate solution to the measured out salting solution. With greater concentrations of dichromate exposure times become increasingly longer. I generally work in the.5% to 2% range.

Image above: Potassium Dichromate Bottles

Sizing

In a good salted paper print the image is sharp, rendering great detail. If the coating solutions soak too deeply into the paper the image will be in the paper rather than on the surface thus causing the image to appear dull and lack detail.

Depending on the paper, I apply a 1-3% (1-3 grams per 100 ml) gelatin sizing. To prepare the sizing add the gelatin to 25 ml or so of distilled water at room temperature. Unflavored gelatin purchased at the grocery store works fine. Let the gelatin bloom for about 20 minutes and then add the final volume of water at 40-50 degrees C. Stir the solution gently with a glass stirring rod. It is now ready to be used.

I pour the solution into a clean print tray and then immerse the paper in the solution. I lift the paper from the gelatin solution and let most of the liquid run off of it back into the tray. I then place the paper, face down, on a piece of thick plexiglass that is resting at an angle and squeegee it with a glass coating rod that is larger than the paper. I turn the paper over and squeegee the surface. I hang the paper to dry on a line that is stretched above my darkroom sink.

As the solution cools it becomes very messy and difficult to work with. I regularly pour mine from the tray back into a pirex cup that sits on a coffee warmer. The optimal temperature for the solution is around 40-45 degrees C and it should not be heated to above 54 degrees C. If there is any sizing solution left over it can be covered and kept in the refrigerator for a few days to be used later after reheating.

Printing

Negative

Salted paper is categorized as printing-out paper and must be printed by contact. Due to the self masking nature of P.O.P. a negative with great contrast is needed for optimal results. Salt prints can render delicate shadow and highlight detail, perhaps better than any other printing process. If you have been exposing and developing your film for conventional silver-gelatin paper you probably don’t have a negative with adequate contrast for a standard salted paper print.

I make enlarged negatives using the Liam Lawless technique of reverse processing of lith film. It is economical and not so difficult to learn. A detailed description of this process is found in the article Less is More by Ed Buffaloe at Unblinking Eye.

Printing Frame

You will need a split back printing frame so that you can monitor your exposures without losing registration between the negative and paper. I use one that I purchased through Bostick & Sullivan and I am very happy with it.

For masking I use red construction paper that is just slightly smaller than the paper that I am printing on. I cut a rectangular opening just larger than the negative and place it on the paper. I place the negative inside the rectangle.

Light Source

The sun is the most readily available light source and gives the best contrast. Drawbacks of using sunlight include variable intensity and long exposure times. It is quite easy to build a UV printer using black lights as the light source. Exposures are fast and intensity is constant. It is also nice to be able to print at night.

Image above: Printing Frame in UV Printer

Exposure

Salt prints need to be exposed well past the point of looking just right because they will become much lighter during the processing sequence. After a little experience you will know when they are right.

Processing

Rinse

After you have determined that the print has received enough exposure take it out of the printer and rinse the unexposed silver. Most of what I have read calls for a simple rinse in running water but my tap water is quite alkaline at about pH 8 and has given me trouble with fog. To be on the safe side I rinse my prints in five consecutive trays of 1% citric acid solution for one minute in each tray. I fill four trays and after I have moved the print to the second tray I dump the first one, rinse it, and refill it. It now becomes tray number five.

Fixer

After the initial rinse salt prints must be thoroughly fixed. Be sure to use fresh fixer. I use a 10% solution of sodium thiosulfate (hypo) adding 2 grams of sodium bicarbonate to each liter of fixer. The sodium bicarbonate helps to hold back the bleaching that takes place and to keep the fixer slightly alkaline. I use two trays and fix for three minutes in each tray. After fixing prints should be immersed in a clearing agent such as Kodak Hypo Clear. I leave my salt prints in clearing agent for three minutes.

Wash

I wash my prints in an archival print washer for one hour and then hang them on a line above my sink to dry.

Salt Print Reducer (Bleach)

• Potassium Ferricyanide.25 gm (one coffee stirrer spoonful)
• Potassium Bromide .2 gm (2 ml 10% solution)
• Hypo 5.0 gm (10 ml 50% solution)
• Water to make  1000.0 ml

Immerse the print in water and then check to make sure that there are no bubbles on the surface. It is then transferred to the reducer and agitated until the desired degree of bleaching is achieved. After reduction prints are treated in a clearing agent and then washed.

Salt Print Toner Recipes

Toning not only changes the image color of the salted paper print but also makes it much more permanent. The following toners can all be used before fixing or after. They all keep well and can be replenished.

Platinum Toner

• Water 400.0 ml
• Potassium Chloroplatinite (20% sol.) 1.0 ml
• Citric Acid 2.5 gm
• Sodium Chloride 2.5 gm
• Water to make 500.0 ml

Place the print in the toner and agitate it until the desired tone is acquired; usually three to ten minutes. If you tone before fixing the print should be rinsed for at least a minute in running water before it goes into the fixing bath. This toner gives a warm gray tone.

Palladium Toner

• Water 400.0 ml
• Sodium Chloropalladite (15% sol.) 2.0 ml
• Citric Acid 2.5 gm
• Sodium Chloride 2.5 gm
• Water to make 500.0 ml

Place the print in the toner and agitate it until the desired tone is acquired; usually three to ten minutes. If you tone before fixing the print should be rinsed for at least a minute in running water before it goes into the fixing bath. This toner gives a warm tone. Palladium toner has a tendency to lower contrast and also to move the color of the paper base from white to cream.

Gold/Borax Toner

• Warm Water (38 degrees C) 400.0 ml
• Borax 3.0 gm
• Gold Chloride (1% sol.) 6.0 ml
• Water to make 500.0 ml

After mixing the toner wait for one hour before using it. Place the print in the toner and agitate it until the desired tone is acquired; usually three to ten minutes. The print can go directly into the fixing bath if you tone before fixing. This toner gives a slightly warm tone.

Gold/Thiocarbamide Toner (my favorite):

• Gold Chloride (1% sol.)  12.0 ml
• Thiourea (1% sol.) 12.0 ml
• Tartaric Acid (10% sol.) 12.0 ml
• Sodium Chloride  5.0 gm
• Distilled Water to make  250.0 ml

Add the thiourea solution to the 12.5 ml of gold chloride solution until the precipitate that forms is dissolved. The quantity of the thiourea solution should be slightly more than that of the gold chloride. Add the tartaric acid to 150 ml of distilled water. Add the gold thiourea solution to the acid solution and mix thoroughly. Last, add the salt and top the solution off with water to 250 ml and stir until it is uniform.

The solution requires no aging; it is ready for use directly after mixing. It tones highlights and shadows at the same rate so the print tones evenly and can be removed from the toning bath at any time. It keeps well and resists decomposition even after moderate use. Tones from plum red to neutral gray can be achieved with this toner.

In conclusion

Everything that I have written here has been tried and proven by me personally. I feel that I have only just begun my exploration of the possibilities of the salted paper process. Salt printing is quite flexible and offers the practitioner a multitude of creative avenues. None of the formulas in this report must be followed exactly and I urge you to experiment and to explore so that you can experience some of the joys and disappointments that our predecessors must have experienced back in the 19th century.