The Light Farm


p. 1 — The Basics

"At one time the photographer's best medium was P O P, printing-out paper, in which the image is visible after exposure and before development. Proofs of negatives were often submitted on paper of this type because the prints would fade if exposed to the light and so the person photographed could not retain the proof print with any degree of satisfaction. He was forced to let the photographer make a print with a more permanent image. For rendition of fine detail, a glossy P O P paper is superior to more modern developing-out papers and for reproduction by means of half-tone engravings, P O P is still recommended."

Handbook of Photography , edited by Keith Henny and Beverly Dudley, 1939.

P.O.P. print — 'Baker's Gelatin Chloride P.O.P., TLF Version #1' processed in 'Hypo & Gold P.O.P. Toner/Fixer', and a ½" crop.

What's different about the P.O.P. workflow? The development step — or rather the lack of one. Actually, in P.O.P. parlance, "development" and "exposure" are often synonymous for the same step. On the other hand, some authors call the toning/fixing step(s) "development." The vocabulary may be confusing, but happily, the workflow is very straightforward.

If you go online to buy a box of printing paper (or shop at a physical store if you're lucky enough to be near one) you're not going to read either D.O.P. or Developing-Out Paper on the box or in the description. Developing-out has been the default silver gelatin printing paper for many years. The type of development is assumed. It wasn't always so. Over the years there have been a great variety of commercial printing-out papers — not only silver gelatin, but also collodion, albumen, platinum, and blueprint paper (cyanotype).

I don't know the history of all the different paper makers but Kodak's last P.O.P. was called Studio Proof, discontinued in 1987. It took a year for Chicago Albumen Works (CAW) to line up Guilleminot, a French firm, to make a gelatin chloride printing-out paper for them. It was marketed under the name Centennial, a venerable name from early photographic history. When Guilleminot closed its doors in 1995, Kentmere Photographic picked up making the paper. That, however, has also stopped and Centennial paper is no longer offered for sale. What this means for us is that if we want to print on gelatin-chloride P.O.P. we have to make our own. Fortunately, it could hardly be easier.

Ease aside, a question that could be reasonably asked is "why?" Number one is because we can — for knowledge's sake, fun, creative potential, or simply niche-marketing. However, there's another reason to pursue this — just as important and I believe growing in importance — its value to museums interested in historical veracity.

The oldest glass plates were exposed and developed for the papers of their times. This meant they had to be very dense and contrasty. This, in turn, means they require a paper with a very long density range. Before digital, museums had to print their old negatives with developing-out paper, as often as not on RC surface (resin-coated) paper. The results were abysmal — chalk and charcoal and neutral blacks rather than the long, smooth density gradients and rich warm tones of printing-out papers.

To a great extent, those problems have been eliminated by digital. Tonal ranges and colors can be accurately reproduced. However, the last step toward true (rather than only "faithful") reproduction involves real paper, whatever the type of paper that matches the time frame of the negative. Thanks to the efforts of the photographers who have worked to bring historical processes into the present, most materials matching is possible today. However, handmade silver gelatin printing-out paper has not yet made it into the "mainstream alt process" lexicon (now, that's a mind bender!) High time it was.


In a nutshell: a printing-out emulsion has more silver than a comparable developing-out emulsion. The emulsion on this page is a case in point. The basic recipe is 'Chloride (Gaslight) Contact Printing Paper' from 'The Light Farm, Volume 1, The Basics', pp. 112-115, and the website tutorials. In addition to excess silver nitrate there is at least one organic compound, which forms an organic salt of silver and that is required for a "genuine" P.O.P.

Silver chloride exposes out to a grayish blue-violet color. Anyone who has left emulsion making glassware out in the light before cleaning up knows the color. Organic silver salts print out a much different color, which varies by the salt and by the light source. I knew this was a different emulsion within minutes of starting to clean up. My emulsion beaker looked like I'd melted rich chocolate in it.

Without toning, the colors are variations on yellowish or reddish brown. Gold toning can change the colors considerably to copper, sepia, or a velvety purplish-brown (my favorite). According to the literature, only platinum toning will give a true black. That's something I won't be trying. There are cheaper ways to get a good black!

Citric acid and sodium potassium tartrate (also known as Rochelle salt) are the most commonly used. The literature also mentions oxalate but I have yet to find a recipe using it.

An important artistic consequence of what is essentially two emulsions in one is that a print often takes on the appearance of split-toning. It can be very beautiful.

The preservation of fine detail is another thing of beauty. One of the reasons a developing-out chloride emulsion (a.k.a. "gaslight" paper) is highly valued, despite its slow speed, is for that reason and the characteristic carries over to the printing-out variation. The crop of the Projection Print Scale (above) shows the sharp and clean density boundaries. However, the density range of the P.O.P. version is a world apart from the Gaslight version. Below left is TLF Gaslight paper in a standard developer and right is P.O.P. from the recipe and toning on this page. A jpeg on a screen doesn't convey it, but there are distinct density breaks between each step. I have recently altered my thirty-year old step tablet by punching three holes and running strips of film tape through the middle of each row. I did this so that I can better judge the density range of materials with ranges greater than the original step tablet. The holes are maximum black and the tape strips are the paper+ unexposed emulsion base color. A chloride emulsion is almost pure white. (Gelatin contributes the faintest of warmth to the white.)

An aside: By comparison, a bromide emulsion is a pale butter color and adding iodide further deepens that color. Developer choice and any toning affect final print color, but the color of the paper the emulsion is coated on has perhaps the greatest influence.

Baker's Gelatin Chloride P.O.P., TLF Version #1
by Denise Ross for The Light Farm, 2017

Preheat one waterbath to 55°C and another to ~38°C/100°F. A waterbath can be pre-heated with any heat source and moved to a non-heating magnetic stirrer for the precipitation step, or heated directly on a heating/stirring magnetic hot plate, or stirred by hand during precipitation and then moved to a pre-heated waterbath. Full instructions for the different methods are in 'The Light Farm, Volume 1, The Basics' and in the web tutorials.

Stage for wet paper coating.


In an 8 oz. jar or 250 ml beaker, dissolve together

Distilled water ... 150 ml

Potassium chloride ... 3 g

When completely dissolved, slowly and thoroughly stir in

Photographic gelatin ... 25 g

Cover the container with a piece of plastic wrap. Let it bloom for 30 minutes. Set the beaker in the 55°C waterbath until the solution temperature reaches 55°C.


In the meantime, dissolve together

Silver Nitrate ... 5 g

Distilled water ... 25 ml

Warm the silver solution in the 38°C waterbath.

PRECIPITATION (a.k.a. "emulsification")

Pour the silver solution through a very small aperture mini-funnel into the side of a strong magnetic stirring vortex. Continue stirring for one minute. (Alternatively, use your favorite precipitation method.)


Ripen 30 minutes at 55°C without stirring.


Solution A:
Silver nitrate ... 5g
Distilled water ... 15 ml

Solution B:
Citric acid ... 2g
Distilled water ... 15 ml

Hold the two solutions in the 38°C waterbath while the emulsion is ripening. Mix together right before adding to the ripened emulsion with slow, gentle stirring (use a clean plastic spoon). Gently and thoroughly stir in 20 drops Photoflo 200. Hardener is not recommended.

Cool to coating temperature (~40-42°C). Coat.

Note: Rives BFK, 250 gsm, white, is my favorite paper. That's especially true for this emulsion and its Gaslight version. The emulsion is gelatin-rich. Heavily sized papers are overkill. The emulsion has to be coated considerably warmer than most other emulsions or it goes down too thick. Too-thick emulsion is almost impossible to completely clear during fixing. This is the same reason to not use hardener in the emulsion. Additionally, plain hypo fixer is far better than hardening fixer.

The recipe is scaled to coat four ½-sheets of Rives, cut down the lengthwise middle of a 22" x 30" sheet of paper. 11" is perfect for coating with a 9" puddle pusher. Rives BFK coats best with 10-12 wraps of Scotch 850 polyester film tape. The single most likely source of problems with this emulsion is being too thick once it's dried on the paper so don't be afraid to experiment with different ways of getting thinner, but still thick enough, coatings. One strip of paper takes 1/4 to 1/3 cup emulsion — give or take exactly how much of the full 30" strip you can coat with your staging.


Once upon a time, printing-out papers were a BIG deal. When gelatin P.O.P. (and to a lesser extent, collodion P.O.P.) grabbed the market from albumen, the same thing happened that happens every time there's a new photo-technology tsunami. Everyone rushed in with advice on the best (i.e. their own) way to do things. There are a LOT of different workflows in the literature. Since this is a "beyond basics" book, I can spell it out — yuh gotta do the work to do the work. There is a strong positive feedback loop between experience and getting good information from historical documents.

The fixing step removes a considerable amount of density from the image. Therefore, it is necessary to expose the print much further than the desired final print.

You can go either of two routes, depending on your printing light source. Before electricity, printing was done by sunlight. "Skylight" studios were designed with printing-out papers in mind. Contact printing frames were designed for visual inspection of half the print without disturbing the registration of negative and paper, and experienced printers really had exposure nailed. Needless to say, we can still do things that way. If so, direct sunlight is not recommended. As I found out the hard way when I was printing albumen in Arizona: negatives cook :-) Not all sunlight is Arizona sunlight, so experiences may differ.

The second option is a UV/"black light" bulb array. With this route, you can make test prints just as you would with any other printing. I used my UV printing box for all the work on this page. Reliable sunshine is hard to come by on the coast of Oregon in the winter. (And I wouldn't have it any other way!)

Either way, expose the print until the highlights show color and/or the blacks look just a bit "bronzed." Left: The print at the top of this page before it was processed. Remember to take print "dry down" into consideration.

After exposure, the print is fixed and then toned, or fixed and toned in the same step, sometimes with an additional plain hypo fixing step before the final washing. You can find countless toning recipes and recommendations. The prints on this page were fixed/toned in hypo and gold chloride, followed by five minutes in plain hypo before washing.

'Hypo & Gold P.O.P. Toner/Fixer'

To make one liter.

Distilled water (~50°C) ... 900 ml
Sodium thiosulfate (hypo) ... 120 g
Gold chloride, 1% solution ... 30 ml

Completely dissolve the hypo in 900 ml water. Depending on how large the hypo crystals are this can take time and continuous stirring. When you are sure everything has dissolved, keep stirring a few more minutes. Continue stirring and pour in the gold chloride. Don't let it splash. Gold chloride is caustic. Add enough water to bring the volume to 1000 ml and stir a few minutes more. Transfer to a glass amber bottle and let the solution rest for a day before you use it. Shake before using.

First off, toning is not required. In its day, the color of an untoned print wasn't considered attractive. That's convention, not fact. Today, when we can make any digital print any shade we wish, I'd like to think we're a bit more open-minded. Let's face it. Gold is expensive. Gold toning adds to the archival life of a silver print, but it's only a matter of degree. A properly fixed and washed silver print is "archival." If we eliminate the toning, and only fix, the recipe gets less expensive to make. It already has twice the silver of a comparable developing-out paper.

Two prints, scanned together. On the left, the print was fixed in hypo (sodium thiosulfate) only. I can find no fault with the color. Having said that, there is tremendous variability in P.O.P. Everything, it seems, has been reported at one time or another to influence the color — the light source, the humidity, the emulsion.... I couldn't begin to claim that I've tried a fraction of the permutations. There might, indeed, be a way to get a truly ugly color. Of course, even that would be subjective.

On the right, a print processed in hypo and gold for five minutes, which is about half the time for full toning. To my eye, that timing maximizes the split-tone effect — one of the reasons for the process.

Left: A print from a different approach. It was toned for a full ten minutes, and it would be hard to distinguish from a conventional selenium-toned print. The color may not be only from the time in the toning bath, however. This print was made with the negative registered with a Pictorico OHP digital negative contrast control mask. The OHP material may have changed the color of the light reaching the paper, and that in turn may have influenced the toned color. (I haven't yet done the follow-on testing.) If you plan on incorporating other materials into some of your printing, it might be wise to use them with all your printing (if consistency matters). Placing an unprinted piece of Pictorico, for example, over each print during exposure not only insures that the color will be consistent, it makes it a lot easier to judge the timing of first test prints of masked negatives.

In the heyday of P.O.P. there were countless varieties. There were different paper colors. Apparently, a favorite color was mauve. I can see that. It would certainly accentuate the spit toning effect. Some varieties were self-toning — the ultimate in speed and ease. Probably most useful were the different contrast grades. The first papers were made to match the expectations, negatives, and work habits of albumen printers. Free enterprise, being what it is, soon added options. With the D.I.Y. options most realistically available to us today, we are probably best off matching our negatives to our paper and not the other way around.

The best negatives are dense and contrasty.

Left: 'AmBr'
Right: 'X2Ag'

Each negative was exposed at a stop slower than normal speed (ISO 6 => 3 and 100 => 64, respectively) and were developed in 4% HC110 rather than my standard 3%. Only the 'AmBr' negative cuts it for P.O.P. printing without help. The top two pirates were printed with that negative. The 'X2Ag' negative had to be masked.

Below left: A print from the 'X2Ag' negative alone, below middle:"invert" and "autocontrast" on the 'X2Ag' negative file, and below right: a digital contrast control mask made from that file.

One note: At least with my printer set-up, the size of a digital mask does not exactly register with its negative unless I re-size. Go to "image size" and uncheck "constrain proportions." I reduced the width by 10 pixels. 12 might be better. If any contrast corrections remain to be made, "curves" or "burn"/"dodge" can fine-tune the digital negative. Applying a Gaussian Blur of about 5 prevents the mask from competing with the detail in the original negative (in contact with the printing paper).

After the toning/fixing step it is advisable to give the print five minutes in a hypo-only bath.

For your reading enjoyment, T. Thorne's original article.


< Paper Negatives      P.O.P., p.2 — Basics Plus >

Copyright © The Light Farm