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Salt Prints on Expired Glass Plates

Glass Plates

In a past post I explored salt prints on expired 4x5 film. I thought this technique should apply to old glass plates. I had experimented in the past with glass plates in the darkroom to various success. I had some old Air Ministry plates from the Second World War which were fogged nearly to blackness. These would be good candidates for experimentation.
Air Ministry Plates Box

Clearing the Plates

My first attempt resulted in a lot of learning :). I soaked the plates in fixer for about 5 minutes until all of the milky emulsion turned clear. I then washed and scrubbed the green anti halation dye from the back of the plates. I then set them out to dry.

Salting the Plate

My first attempt at this was to wet the plate thoroughly with my 2% salt solution with no citric acid. More reading indicated perhaps sodium citrate but not citric acid. I did this with a small piece of sponge giving what I though was ample time for the salt to soak into the emulsion. I then dried the plate.

Sensitizing the Plate

With the dried salted plate I then applied the silver nitrate solution by pouring a small amount on the plate and then distributing it using a small piece of sponge. As the emulsion swelled I had to be careful to not remove or tear the emulsion. I would pour more solution out and work it into the emulsion. I then squeegeed away the excess being careful to use gloves to keep it off my skin.

Next I exposed the plate on an overcast day. Previously I had full sunlight and could expose for 6 minutes which worked out well. Now I tried it by eye. Occasional rain caused me to interrupt what was probably at least 15 minutes of exposure.

It was apparent when looking at the negative sandwich that there was a lot of splotchiness. I could discern places where I had pooled the silver nitrate on the glass pate and lots of streaking.  The result is shown below.
First attempt

 So my next attempt I revised my methods. I would soak the plates in each solution for at least 5 minutes to allow a complete and even absorption into the emulsion. This proved more effective. A full immersion in the salt solution as above, followed by drying then sensitizing by placing the plate in a shallow dish not much larger than the plate. (100ml of silver nitrate solution just barely covers the plate.). This was in turn dried. I felt satisfied with the result as the emulsion took on a milky tone similar to ortho film or what the plates looked like before I soaked them in fixer.

Again I made my negative sandwich and exposed the print for what I thought was sufficient time looking at the back side of the plate. I soaked the plate in salt water then fixed it. The result was much better. The print suffers from a negative with too little contrast. However the result was even across the entire negative. See below....

Some flaws are apparent. The black patch in the lower left is probably an area where the original silver emulsion had not been completely fixed away before the sensitization. The white blotches are where mold had attacked the emulsion . Below you can see the tell tale tendrils as the mold grows and eats into the emulsion. There is also a scratch of unknown origin (perhaps from the squeegee).

Mold in the emulsion
So it is clear the new techniques hold promise. Plates with less problems with the emulsion should create good results.
Below are some other plates. These I dried after sensitization on the plate warmer on the hob under a small box to keep the light off. The temperature was about 50C and did not seem to adversely affect the results.
Snow scene at night
 This is a photo my grandfather made in New England. After having a negative adhere to a plate I printed this emulsion side away from the plate, some softness is seen as a result. There are a few blotches and flaws I attribute to excess silver nitrate on the emulsion. The exposure was good (10 minutes strong sun) with a small amount of bronzing in the tree trunks though not apparent in the scan.
This print has a scraped piece of emulsion and some blotching. The exposure is really good and shows great range.
Young Tom
 This is another photo my grandfather took this time of my dad in the desert around Phoenix. This one was underexposed (6 minutes) and has some dark blotches.
Young Tom 2
 This is another photo my grandfather took of my dad. This time I ran a 15 minute exposure. Much bronzing was present (see warnings lower down) though not apparent when viewed from the non-emulsion side.  I oriented the negative to avoid the large blot on the left. This was created by a wet plate in contact with a negative.

Selenium Toning

I did a  couple of simple experiments using selenium toning. Normally gold or palladium toning is recommended for salt prints. I don't have any however. At first I tried 1+19 dilution and soaked one end of the plate before immersing it all. This segment is still apparent even though I left the plate soaking for at least 10 minutes. The color turned cooler or more gray and the image darkened as well.
Selenium Toned 1+19
 Next I toned the same plate with selenium 1+3. Here after just a few minutes the image turned very light. 
Selenium Toned 1+3

Newer Ilford Plates

Given the trouble I had with these very old plates and particularly mold, I opted to try again with new Ilford plates. I don't know their age but when inspected they showed no signs of mold.
Ilford Plates
I sensitized and exposed these plates in the same way as the others. The results that I got were more satisfying.

Stopping the Plates from Sticking

These plates were very susceptible to sticking to the negative. This scared me enough to try something drastic. I stretched a piece of cling film or saran wrap over the plate's emulsion before placing the negative on top. This worked really well as I cannot discern any visible effect on the image and I could place my negative safely emulsion side down. 



Exposure is unusual to judge on plates. One tends to look through the plate into some light source or a white wall. However when you mount the plate 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 plate 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 plate. This means a seemingly under-exposed plate will be OK once mounted on paper. One can also experiment with different backing materials and use the transparency effectively.

I did find one case where the sensitized emulsion had not dried properly and stuck to the negative emulsion which was very difficult to peel apart. It would have been better probably to soak them apart to avoid the chance of ruining the negative. However a side effect of this was that the glass plate took on a brown tone wherever it stuck to the negative. And over time the negative also acquired a brown tone.

I believe that using a squeegee to remove the excess silver nitrate when sensitizing is very important to achieve consistent results.  Any blotchiness seems to be the result of pooled or excess silver nitrate on the emulsion. The difficulty is that the squeegee can remove or scratch the emulsion if one is not careful. The same may also be true of applying the salt. I squeegee the back of the plate to remove excess silver nitrate but this is mostly to conserve and expensive solution. Any chemicals on the back of the plate wash off in the fixing and washing processes.

Bronzing is a well known effect when the salt print is over-exposed. It results in a greenish tinge in the over exposed areas. If viewed from the emulsion side the bronzing is apparent and detracts significantly from the image. However because this is a transparency when viewed from the other side of the plate the bronzing is no longer apparent. This could be an advantage over paper salt prints.
Young Tom 2 Bronzing example