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Salt Print Transparencies on Expired Film

Always interested in trying something new I decided to try salt printing the predecessor to black and white film photography. I did the usual perusal on the web

And many other articles a Google away. Basically salt (kosher or sea salt as we shall see later) and silver nitrate. Citric acid is helpful.

While reading about traditional paper-based prints one sees an emphasis on using sized paper. Now sized paper typically means a gelatin (or other material like arrowroot) coating. The sizing allows the silver image to sit on the top of the paper fibers rather than in them. This is seen as producing a sharper image. Some however prefer the un-sized paper as they like the depth of the image.

In reading this it occurred to me that photographic film is really just sized plastic film. I have a few boxes of expired 4x5 film. I thought I should try to use them as a salt print medium. I would take the unexposed sheets and plunge them directly into fixer for 5 minutes to remove all of the silver. Then I would have to thoroughly wash and dry the film. Then I should have nothing but gelatin coated plastic film.

Well I finally got around to trying out my idea. Like most starts this one was fraught with problems and errors that also show the promise. My first mistake was to use table salt. Table salt has additives that are used as anti-caking agents. Mine has Sodium Hexacyanoferrate III. The next was to assume that gelatin only coated the emulsion side of the film. It didn't in this case, it was on both sides.

So when salting the film I let salt get on the back side. Later when the salted film dried I made the same mistake with the silver nitrate solution. I reasoned at the time it would all would easily clean off the Mylar surface. With paper in salt printing one has to be careful to keep the chemicals off the back of the paper as they get absorbed and can lead to undesirable staining of the image. I thought my method would be immune to this. What happened was an uneven coating on the back which had emulsion. Some of this coating exhibited a bright blue color. I reasoned this was the anti-caking agent losing its sodium which bound to the nitrate of the silver nitrate to create sodium nitrate and Prussian blue.  In some areas though the salt and silver nitrate created silver chloride in what I assume were areas with different chemical equilibrium. These in turn created brown pools.

As seen below the image shows great promise however and so encourages me to correct some of my obvious errors.

Saxophone Salt Print on 4x5 film (Glenn Morse photo) Exposed for 6 minutes.

The next attempt I mixed a fresh batch of salt. This time 2% sea salt (2gm per 100ml) with 5gm of citric acid. I also added 4 gm of citric acid to the 12% silver nitrate solution. I added it to the salt to neutralize any buffer that might be in any paper I had (I was also testing on paper at this time). Citric acid in silver nitrate is supposed to help it keep longer.

Now I washed thoroughly the 2 remaining pieces of silver-free film I had already coated with the old salt solution. I did this by soaking them in fresh water then drying them. I then re-coated them in salt this time by soaking each sheet for 3 minutes in the new salt solution to allow the gelatin time to swell and absorb the salt water. I squeegeed the remaining salt water away to prevent excess salt deposits on the surface. These I then set in the warm sun to dry. Though this meant salt was again on the back of the film I reasoned that as long as I kept the silver nitrate off of the back I would be OK.

Next with the dry film I taped them down emulsion side up (film notches in the upper right corner) to a sheet of Plexiglas with tape around the entire periphery to seal the back side of the film.  I then dipped a small piece of sponge in silver nitrate and rubbed the solution across both pieces of film. I did this repeatedly and tried to make sure the gelatin had swollen and taken the silver nitrate. I then squeegeed away the excess being careful to use gloves to keep it off my skin. These I then set in a dark cupboard to dry.
Film taped on Plexiglas with silver nitrate applied. Note each has its own tint. This because the original film sources are different.
 Next I removed the dried film and taped the negative on top as shown.
Negative hinge-taped to sensitized film.

 Then I clamped the negative under a sheet of glass to place in the sun.
Ready to put in the sun. 
I let the first one exposed for 5 minutes under direct sunlight. Unlike paper I can inspect the exposure without taking the print from the frame. The fact it is a transparency and mounted on Plexiglas means I can look at the underside to judge the exposure. After a few minutes the characteristic orange brown color appears.

Exposed film and negative sandwich.
The print as it emerges from the sunlight. 
A clear image emerges and none of the pools of brown from my first attempt. I then washed the print first in a bath of sea salt and citric acid where a milky substance of undeveloped silver and salt (silver chloride) washes away. I then washed about 5 minutes in water before fixing for 5 minutes in hypo fixer. Followed by 5 minutes water wash, 5 minutes hypo clear and then 5 minutes final wash. The result  below.
Final salt print transparency 5 minute exposure. 
The result is very pleasing. I made a second print with the remaining sensitized sheet. This sheet was was troublesome. It exhibited what looked like mineral deposits and cloudy areas when dried after sensitization.
Second film with cloudiness and deposits visible. 
I exposed this one at 10 minutes (direct sun) to see what would happen with a longer exposure and the undeveloped result is one that is mottled and almost looks bronze which could indicate over exposure. It is pretty in it own way.
Undeveloped second film with 10 minute exposure.
Washing and fixing gives this result.
Finished second salt print 10 minutes exposure. 
This second emulsion was a bit more tortured and perhaps torn. These last two had gone through a lot of soaking and handling which isn't helpful. Also each film was sourced from a different negative film. The last one from old Ilford Ortho film, the previous from old Ilford FP4+ and the first from Ilford FP3. Each probably has a different emulsion coating as they all had a subtle color hue fro
m yellow to pink to blue.

I think the results are great and with some clever mounting could be very effective.

Here is the previous print mounted on white paper for contrast and framed. It is a small jewel to behold as it holds a great deal of detail and carries a warm metallic sheen to it.
Framed Salt Print Transparency

Exposure Judgement

Exposure is unusual to judge on transparencies. One tends to look through the transparency into some light source or a white wall. However when you mount the transparency on white paper it will be darker and I would wager by exactly one stop. When mounted with the emulsion directly against the paper the light must travel through the transparency before reaching your eye. This makes the attenuation of the light twice that when viewed using a distant wall where the light only passes once through the transparency. This means a seemingly under-exposed transparency will be OK once mounted on paper. One can also experiment with different backing materials and use the transparency effectively.

A Couple More Examples

Two more photos from my Grandfather Cushman Morse.

Picacho Peak