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SALTED PAPER

© 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 another:



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.



Paper choice

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.


Correct exposure

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 nitrate order had not come in, so all of this work was made from raiding years-old VDB and salt kits. I have since found out that silver nitrate, as long as it does not come in contact with an organic, lasts indefinitely.

Miscellaneous advice, do as I say, not as I do

  •  Be rigorous about processing and cleaning the work area; leftover spills on the counter and inadequate fixing (which I didn't worry about enough when printing step wedges) will develop stains like this immediately.
  • Be sure when brush-sizing/salting, that you actually size/salt every sheet of paper, and don't forget and double-salt a piece or this is what you'll get.
  • Store silver nitrate in an appropriate brown glass bottle, and not in a vitamin bottle that has a plastic cap and gasket, no matter how lightproof. Something in the cap/gasket reacts with the silver nitrate (source, Alberto Novo). Below is not a picture of my colon, but the inside of my gelcap bottle.
  • Watch that there is no black silver particulate in your brush from storing the silver nitrate in an improper container (pill bottle) where it has a chance of coming into contact with an organic.
  • Silver nitrate, unlike platinum, VDB, or cyanotype which are all various shades of yellow,  is clear and difficult to see on the paper so use a drop or two of blue food coloring in the silver nitrate sensitizer to be able to see where you've coated.
  • Pour the silver nitrate sensitizer carefully in a line on one edge of the paper and immediately brush all over the print; don't pour the sensitizer in the center and then brush because uneven absorption of the sensitizer can occur.
  • Make sure the coating is evenly applied and there is no chance of extra silver nitrate from the edges blooming back into the image area as you can see below.
  • After multiple coating fiascos I have switched to a synthetic bristle, 3" wide brush. It coats more smoothly and predictably. I got mine from Tsyoshi Ito at projectbasho.org, Otherwise I use a foam brush from the hardware store with edges trimmed round, or cotton balls.
  • Do not go outside between exposures and sunbathe on the first nice day since Nam, because that sun will find every splatter of silver nitrate on your hands, arms, and clothes and turn it a beautiful chocolate and very permanent brown.  Well, make sure to wash your hands before going outside in other words!
  • The sun is the best way to expose salted paper (unless doing calibrations which require more exact timing). It produces wonderful color and contrast, and to increase contrast face the frame toward the north sky or cover it with several layers of tissue paper. But, the best alt pro gadget I have ever bought is this UV meter from LightMeasure.com (long wavelength). I used it to measure the "dose" of UV for my salted paper under the UVBL lightbox and now I can print outside at any reasonable hour of the day from AM to PM (we printed at 7PM!) as long as I match that same dose. So now I really have to stay nitrate-free! How about printing by the moon? Salted moonprints anyone?
  • Any spills anywhere have to be cleaned up right away, because that drip on your brand new white bathroom sink will soon expose to a nice permanent brown that will not make your spouse happy. I have been counseled to use diluted Chlorox mixed with table salt to remove said stains by Alberto Novo, a chemist from Italy (I love my smart friends) or Farmer's Reducer.
  • Do NOT iron a finished print on the cotton setting if it has gelatin on the surface (doh) because it will scorch like a campfire marshmallow. Score one for not using gelatin.


  • Always agitate while in each bath, especially the fixer, or else you'll get a lovely dark bubble mark like this one. Also, this print, another throwaway, was made on paper I had salted 10 years ago. Both attempts at printing on this paper fogged immediately in the salted water bath, so my guess is, since I had not seen that happen on freshly salted paper, that 10 years is probably a bit on the stale side.
  • Here is another fiasco (how many more can there be?).I thought it was chemical contamination until Kees Brandenburg informed me of the real reason: I blew-dry the print unevenly so that the paper was irregularly dry although the whole paper felt dry to the touch. Hence, after blow-drying, let the paper sit for a while longer before exposure so any remaining moisture will even out.
  • Be sure to CHECK YOUR NEGATIVES for pizza wheels when there are large areas of highlights in the negative (e.g. clouds, sky or fat bellies) before printing a series of 10 or more prints (yep I did this)  to find out via the scanner that lo and behold, little teeny black dots are marching across the image. Under Advance Media Control Increase Drying Time per Pass to 20-50, Paper Thickness to 15, and Platen Gap to Wider and use Pictorico Ultra. Or use the front load feeder of the printer as many have advised me.
  • Now this one is not on me. A particular paper, when it went into the salt-size bath, looked like it got an instant case of measles. I was sizing 4 different papers at once and this was the only one that did so. I wll print on this paper anyway but I have never seen anything like it and my prediction is it will print spotty.
  • And here is how it printed. Which is why I am drowning my sorrows in a box of chocolate. Probably easiest to see it in the top right corner in the darks.
  •  
  • Even though those black dots are staying there, white dots can be conveniently colored in with Prismacolor French Grays or Warm Grays, and dark areas are very much the color of Prismacolor Sepia.
  • This is how I felt about salt after six weeks of fiascos, but thank God my humor is still intact:
  • And my final hurdle is to a) buy VueScan software, b) buy color calibration sheets and c) calibrate my Epson V750 scanner so it will actually read the correct color of the salt print (ruddy brown); very difficult to capture it via scanner without color calibration! Note the reason why, according to Wolf Faust who makes color targets to produce ICC profiles for scanners, etc.: it's silver's tendency to metamerize, as can be seen in the image below with the red/green shimmer in an overexposed square of a print.
  • And here is a visual of what the scanner sees (middle strip) and what it more looks like (outside edges) in contrast and color.
 
  • I found a toner I am in love with: gold-thiourea. Note the luscious pinky-red tone in comparison to an untoned salt print.
  • And here is a comparison of plain salted paper and ammonium chloride/sodium citrate/gelatin salted paper, both toned in thiourea-gold. Note the luscious taupey lavender of the plain salted paper, and the more ruddy brown of the gelatin sized one.


  • I found the perfect frame for salted paper prints; it is a small-profile frame only 9/10 inch wide, and it has a 1/4 inch tarnished silver inset. Larson Juhl Black&Silver 334916. Now if my prints were only as perfect as the frame I'd have died and gone to heaven.
 

In summary here is my process to date:
 
1. Tray salt. The best way I have found to get even salting. 8g gelatin, 20g ammonium chloride 20g sodium citrate per liter. OR 40 g ammonium caseinate, 20 g sodium chloride 20 g sodium citrate in a liter. 
2. Hahnemühle Platinum Rag.
3. Color the silver nitrate with blue food coloring to see the coating.
4. Use a synthetic bristle brush, soaked in distilled water first and coat up to 6 pieces at once and then soak the brush again in distilled water until all black precipitate falls out, soak again, and dry. When using said brush, whisper-coat.Or, use a sponge brush with the corners cut and rounded, OR cotton balls.
5. Expose dry. I let it sit for even up to 2 hr in 25% humidity. I sometimes carefully blow dry it evenly and then let it sit some more before exposure. Plain salted paper will fog more quickly though, because it doesn't have citrate in the paper to slow down fogging.
6. Expose for 24-38 minutes in UVBL with a +30-50 negative and a 50% hybrid curve in CCIII but I realize that all has to be checked every now and then because there are many variables such as thickness of sizing, amount of salt to silver, paper, etc.
7. 5% salted water wash for three trays of 4 minutes each (last tray no salt), agitating continually.
8. Tone at this stage for 3-15 minutes, and if toning, use an extra plain water bath between the salt water and the toning bath.If the toner of choice is acid (e.g. platinum) make the bath between toner and fixer alkaline with sodium carbonate or baking soda. If using thiourea, use another salted water wash to return the print to normal.
9. Fix in Photoformulary’s alkaline TF-4 fixer for two trays of 2 minutes each agitating continually (no bleaching) (ammonium thiosulfate fixes are twice as fast as sodium thiosulfate so fix 4 mn each tray for the latter).
10. Water wash
11. 1% sodium sulfite bath for 4 minutes.
12. Wash for 30 minutes to a couple hours..

This summary is one of observations, advice, and not firm conviction. I am not a scientist nor a chemist, but I was raised by a consultant metallurgist physicist father and an artist mother. This has completely informed my working methods, an odd mix of rigid and loose, as my students might attest. My goal is to answer questions for myself and then translate those answers to students at the college level, or workshop participants who are much less homogenized than college-age juniors pursuing a 4-year photography degree. I may geek out at all this testing. Generally photographers just want to make prints and could care less. But maybe my observations will help make the salted paper process easier, more approachable, and enticing. At the very least, below is a visual that shows where I started and where I ended in the calibration process, an indication of how important it is to take the time to develop suitable negatives to fit the incredible salt exposure scale. 


 

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