© Christina Z. Anderson 2017
All of this, below, was written a year ago when I started intensive salted paper research. My research through 180+ texts has resulted in a book entitled Salted Paper Printing, A Step-by-Step Manual Highlighting Contemporary Artists that will be available from Routledge in September 2017. It is already available for preorder on Amazon. At the very least this book has a wonderful Troubleshooting Salted Paper chapter in which are 70 images of my, and others', glorious mistakes! The book will be almost everything you want to know about salt but the kitchen sink. So stay tuned for exciting tidbits on salted paper printing.
Salt has an exposure scale rivaling platinum and a beautiful ruddy color. I call it the “poor man’s platinum” because of its minimal cost. Salt is a POP or a printing out process as opposed to a DOP or developing out process. As shadows get darker and darker during exposure, they hold back light and slow down in exposure. The shadows, therefore, don’t block up while the highlights are printing. And as for cost, silver nitrate is about $1 per gram and 15 grams will easily make 20 8x10 prints. Here is a comparison of a platinum print, top, with a salt print, below, and to see my salted paper portfolio click here.
And here is a salted paper/tricolor gum print comparison (note: image is a yellowed print from the 1950s):
I returned to salt after a 10-year "neglect" of the process to answer one question prompted by an Internet discussion: which makes for a better print, to salt the paper with or without added gelatin. I had seen some really flat, unappealing salt prints that were done without gelatin and assumed the lack of gelatin was the cause. Now I know that the cause is paper choice, exposure, and matching one's digital negative curve to this incredibly long exposure scale.
I also returned to salt with ten years more alternative process experience under my belt, and thus my questions increased from the initial inquiry to the following list:
- Gelatin or not (at the very least this makes a big difference to vegans)
- Paper choice
- Correct exposure
- Correct custom curves
- Simplified methods of processing
- Fixing and its inherent potential for bleaching
- Shelf life of chemicals, etc.
- Toning options
But first, why is it the best of times for salt today?
I pulled out every book I own that has a salted paper chapter (now 80+). Many have pictures, and often a salt print is very low contrast. In the historical literature it was characterized as being dull and "dead." Toward the 1890s when matte paper became the rage, salt had a rebirth in popularity, but still I see this dullness in many salted paper works. I think I know why. It takes forethought to expose and develop a film negative to accommodate salt's huge exposure scale (see below), and then the negative becomes too contrasty to use for other processes like gelatin silver. Many books attest to the fact that a normal negative is useless with salt. With digital inks, the contrast range is so great that finally there is an easy "negative" that is perfect for the salt process. WIth some time spent choosing a correct, and long, printing time and calibrating custom curves, we can finally see salt's true nature, with an exposure scale longer than platinum. Note a comparison of a typical salt image in books and a scan of one of my recent salted paper images.
Gelatin or not
Salt does quite well without gelatin on a suitable paper, as long as one calibrates curves for that method. My curves are calibrated for the use of gelatin, with the salts embedded in 0.8% gelatin, and my negative printed on paper without gelatin is too flat. There is slightly greater dMax with gelatin, similar to the dMax difference between glossy and matte B&W paper, and I print with both glossy and matte B&W and my curves for each of those papers are different, too. The only way someone would notice this difference is in a side-by-side of the same image, which will never happen. Conclusion: choose one or the other method and go with it. Actually, after a year of salted paper research, my favorite sizing ingredient is not gelatin, but casein!
And below is an image comparison of plain paper (left) salted with just table salt and paper salted with a combined gelatin/ammonium chloride/sodium citrate typical salting bath (right).Note the color and contrast difference between the two. These images were also gold-toned in a thiourea gold toner for 6 minutes.
I calibrated Hahnemühle Platinum Rag and the new Lanaquarelle after printing on a total of eleven papers. Hahnemühle is incredible for salt: sharp, white, crisp. I have setttled on HPR and the new Platine as my two salted papers of choice. There are some other good, and inexpensive, papers out there suitable for salt and all it takes is a simple Stouffer step wedge print to determine this. Arches Cover, Coventry Rag, Bee, Bergger, and Arches Platine all performed admirably, too. Below is, from left to right, Bergger, Hahnemühle, Bee, Arches Cover, Coventry Rag, and Weston.Where grayer, Nelson gold toned. Strips are from the dark side of the Stouffer step tablet, and do not include the highlights.
My humidity is extremely low here, 15-25%. The paper was exposed bone-dry. With platinum/palladium low humidity is an issue. I get about 8 stops/24 steps on a 31-step tablet in my conditions, where others will get, say, 11 stops. Other processes are much less than that. I assumed salt would have an exposure scale similar to any silver process. This is a completely erroneous assumption. It is not an iron-silver process but a chloride-silver process, and silly me to think such different chemistry would perform the same.
Choosing a standard printing time (SPT) for salt is not an easy choice to make, being that it is a POP process, which means as the shadows are printing in they get darker and darker and slow down while the highlights continue to print in at the normal pace. Thus, greater exposure can lead to a more gradual tonal range in the exposure scale, aka a lower contrast print.
I noticed that, in essence, there might still be steps of dMax "to be had" by looking at the borders of the step wedge where the negative ended. There was still a line of demarcation. I exposed the step wedge up to a 1-hour exposure, and the print got richer albeit flatter. This forced me to buy a 41-step tablet (log 4.1 vs log 3.1). Sure enough, at 27 minutes the 41-step exposure scale is 36 steps, more than a 31-step tablet can handle. See below.
There is a middle ground where it is dark enough in the shadows (convincing “black”) even though there may still be lines of demarcation between steps, and highlights are still bright, taking into account the maximum negative density digital printers can produce. After multiple calibrations of exposure times I settled on 24 minutes with +30 ink density, or 38 minutes with +40-50 ink density on Pictorico Ultra.
Correct custom curves
I calibrated a set of contrast curves. My preference in the CCIII system was a 50% hybrid curve which is contrastier than a linearized curve, and this makes sense: the longer the exposure, the more subtle the contrast between steps (for CCIII see here: http://www.precisiondigitalnegatives.com ). In the visual below the added contrast boost of the shadows can be seen in the slight upwards curve at the top right. Note how different the curves for salt are than for platinum.
Note how important calibrating a custom curve is; image on the left is curved, image on the right is straight out of the printer with no curve.
Simplified methods of processing
I used tap water this time instead of distilled in my salted bath and fix bath and water wash: the sky didn’t fall down and all was good.
Fixing and its inherent potential for bleaching
I ran out of sodium thiosulfate crystals so I used Photographer’s Formulary TF-4 Archival Rapid Fixer (http://stores.photoformulary.com/tf-4-archival-fix/). It is an alkaline fix, already mixed, and does not require hypoclear. Priceless. No need to mix up sodium thiosulfate penta crystals. $14 will give you concentrate to make 1 gallon of working strength fix. I mixed it B&W paper strength and there was no bleaching with this fix. Salt can be very confusing because of all the color shifts it undergoes with processing. It comes out of the exposure unit very dark and purple-brown. It hits the first sodium chloride water bath and turns immediately pale yellow-brown. Then when it enters the fixer it immediately darkens to a more contrasty chocolate color, and finally when it dries it changes to its final much darker, duller red-brown. In other words, there are so many color changes throughout the process it is easy to assume bleaching occurs at any one step. I tested this by fixing much longer, for 20 minutes. Still no bleaching.
Shelf life of chemicals, etc.
I was desperate; my silver n