POP in a nutshell
Printing-out paper, or POP, evolved from albumen papers, which was by far the dominant type of photographic paper used for the first seventy-five years of photography. Eventually gelatin replaced albumen as the "substrate" to which the photographic emulsion, in this case silver nitrate, was applied. POP prints became hugely popular around the turn of the 20th century, as photographers working in city studios could offer their clients "instant" portraits on paper which could be processed without requiring a darkroom.
POP has several distinct advantages over developing-out paper. First, as previously stated, it can be "processed" in subdued room lighting (daylight with shades drawn or incandescent - not fluorescent - bulb). Second, the exposure of the print can be monitored as it is printing. Third, the paper has an extraordinary tonal range, allowing very deep shadows and quite bright highlights to be printed with detail.
Photographers today have the choice of creating their own POP by coating presized paper with salt, either albumen or gelatin, and silver nitrate or by buying manufactured POP. Centennial POP by Chicago Albumen Works is currently available through Bostick & Sullivan for $59.30 for 50 8x10 sheets, and is a wonderful fine art paper with a glossy finish.
Requirements
Printing-out paper requires several items somewhat unique to alternative processes. The first requirement is a negative with a density range of 1.8 to 2.0, as the extreme tonal range of POP paper will cause a "normal" negative to print very flat. The second is a contact printing frame with a split back, which enables monitoring of the printing-out process. Third, some sort of toner is needed, usually gold or selenium, unless a brown-orange print color is desired. The fourth requirement is a bright, sunny day, since POP is very sensitive to ultraviolet light, and the best source of this radiation is the sun. The last (absolute) necessity is patience...and lots of it.
Chemical preparation
The only chemical that is absolutely required for processing POP paper is plain non-hardening fixer. Kodak RapidFix (without the hardener - part b) is a suitable product. Remember: only use part A of the product; the hardener will ruin a POP print by severely over-bleaching it. Dilute the stock solution with water to create a 1:7 working solution. Two fixing baths are recommended, using the typical rotation method to avoid exhaustion of the fixer.
If a print tone other than ugly orange is desired, a toner should be used. Here are several popular toning formulae:
Two-part gold thiocyanate
These stock solutions have an indefinite shelf life.
Stock Solution Part A Part B Distilled water 490ml Distilled water 500ml Gold chloride 1% solution 10ml Sodium thiocyanate 10g
Upon mixing parts A and B the solution will turn a bright red color, which will quickly dissipate to yield a clear liquid. This is the working strength solution to be used for this session only, as gold thiocyanate is quickly rendered useless by oxidation. After toning each 8x10 print, add 8ml of each stock solution to maintain consistency. Tone print before fixing.
Working Solution Distilled water 900ml Part A 50ml Part B 50ml
Gold borax
This toner keeps well, may be reused and can be replenished. Experiment with different strengths of toner to expand or contract toning times. Tone print before fixing.
Stock/Working Solution Distilled water 350ml Gold chloride 1% solution 6ml Borax 3g Distilled water to make 400ml
Selenium
Experimentation will be required to hone selenium toning, which can be finnicky. One is better off toning too slowly than too fast, so a low concentration is the prescription for best control. Fast toning in selenium can produce interesting split-toning effects. Tone print after fixing.
Stock/Working Solution Distilled water 500ml Kodak Rapid Selenium Toner 1-2ml
Pour toner and fixer into trays one size larger than the paper being used (11x14 tray for 8x10 prints). Ribbed trays may be used; however, the prints must be constantly agitated to avoid having bright lines form where the paper contacts the tray. Flat trays do not have this problem and are better for fully submerging the print, since, to avoid waste, small amounts of toner are used.
Exposing POP
Loading - This step must be performed in subdued light. Load a contact printing frame with paper and a negative in typical fashion. (Place the back, spring side down, on a flat surface. Place the paper to be exposed on top of the back, emulsion side up. Place a negative on the paper, emulsion side down. Cover with the (CLEAN) glass from the print frame. Place the frame on top of the entire assembly. Flip the frame over, so that the spring side is facing up, and clamp shut.) Once the assembly has been examined for straightness, cleanliness, etc., place the print frame in the sun for printing.
Printing - The amount of time required to fully print out a silver chloride print will vary depending on the strength of the light source (by the way, UV printers may be used in lieu of the sun) and the density of the negative. Some prints will take as little as a minute or two, while others may take 15 to 20 minutes to produce. The summer sun, since it is much higher in the sky than it is in the winter, will dramatically shorten print times. Prints may also be produced by placing the print frame toward open sky, which yields higher contrast images but takes considerably longer due to the lack of direct sunlight.
After some time has passed, remove the frame from the light source, and open half of the split back of the print frame. Incredible! This is why it's called printing-out paper! The image already exists on the paper, but this is where the process gets tricky. Toning and fixing will bleach the print somewhat, while drying will darken it. A little trial and error is required to determine when to stop printing. The general rule of thumb is to print until the highlights start to show detail. The shadow areas will appear quite dark most likely but will bleach more than enough to show detail. The toning procedure being used should also be considered at this time. Toning in gold before fixing is rather straightforward, and follows the aforementioned rule of thumb. Toning in gold after fixing will require exposing the print to light until it is considerably darker than one would think is "normal". This is because fixing the print first will bleach it much more than toning first. At this point it should be mentioned that when using selenium toner, the print should be fixed BEFORE it is toned, otherwise the toner will react with the silver chloride in the print and will make the print "fuzzy" in appearance.
Processing POP
Rinsing - Once the print has been exposed to an acceptable level, remove it from the print frame and rinse it in running water. The water will be murky at first as unreacted silver salt is rinsed away. As it is rinsed the print will turn from a bluish-purple color to an orange-brown color as the reaction is stopped. This will probably take about 30 seconds but should be continued until the water is clear, as excess silver will quickly exhaust the toning solution. If a small print is being made on larger paper (and the dark edge will ultimately be trimmed away), trim any excessive dark border from the print. There is no point to using (and wasting) precious gold toner on paper, which is going to be discarded anyway.
Toning - After rinsing, slip the print into the toning solution, and watch for a color change while agitating. Usually toning times run anywhere from three to twelve minutes, with the longer times producing the coldest tones. The thing to keep in mind here is that the color of the print while it is in the toner has little to do with the ultimate color of the print. Watch for the amount of color CHANGE to determine when to stop toning. (Yes... more trial and error.) After a few attempts instinct will guide the process.
Fixing - Prints should be fixed in two baths of non-hardening fixer for approximately 5 minutes each. As they are being fixed, the prints will experience yet another color shift, which will closely resemble the look of the final print. Bear in mind that a considerable dry-down effect will impact the final look of the print. If a print looks great while sitting in the fixer, it is guaranteed to be too dark once dried.
Washing - Before washing, soak in a hypo clear (use Kodak HCA or one tablespoon EDTA plus one tablespoon sodium sulfite to a gallon of water) bath for two to three minutes. Wash prints for 60 to 90 minutes (only about 30 minutes is required if using hypo clear) in running water, preferably in an archival print washer. One of the undeniably great virtues of POP is that a properly washed print will outlive the artist who produced it (as well as his children and his grandchildren). Silver chloride prints exist today which were produced over 150 years ago and have withstood the rigors of time with amazing permanence. Hang prints to dry, and straighten in a dry mounting press.
Alternative toning methods - If selenium or gold toning AFTER fixing is desired, rinse and fix the print as described above, then fully wash. Once the print has been washed thoroughly, tone in either gold or selenium. Then wash again for another 30 minutes. This method of toning is not necessary for gold, but is absolutely required if toning in selenium. Keep in mind that prints produced using this method will be vastly different from those created using the standard method of toning. (The difference is in the point at which bleaching occurs.)
Consider toning with tea or coffee as well. Steep five or six tea bags (no need to use any elaborate blend; the standard orange pekoe will do fine) in a quart of water. Let cool, and tone away. Surprisingly teas and coffee are archivally permanent but may require extended washing.Conclusion - As already stated, toning is not actually required to produce a fine POP print. The color may not be all that pleasing, but a fixed, well-washed print can still be a thing of beauty and archivally permanent.
Enjoy.