The chapter called “Palladium” of Sarah Van Keuren’s book “A Non-Silver Manual: Cyanotype, Vandyke Brown, Palladium & Gum Bichromate with instructions for making light-resists including pinhole photography”.
Palladium and platinum rely on iron salts to react to light, as do cyanotype and vandyke. Upon exposure to actinic light, iron salts are reduced from ferric to ferrous and during development palladium salts that lie in contact with the ferrous salts are reduced to visible palladium metal. The color of a palladium print can range from brown tones that can be confused with vandyke to gray tones that can be mistaken for platinum, depending on the developer that is used.
Palladium and vandyke produce prints with long, delicate tonal scales. However, unlike vandyke brown, the contrast in palladium (and platinum) can be controlled somewhat by two or three means.
Palladium, like gold and platinum, is a ‘noble’ metal that does not tarnish. It is possible to etch away, with hydrochloric or citric acid, residual iron salts that remain in the paper after a palladium print is developed. This leaves you with an image that is pure palladium — but the acid attacks the paper fiber. In recent years a chelating agent, EDTA, has been used instead of acid to remove the iron salts. It is gentler to the paper fibers than acid. Prints cleared with EDTA will not fade or become brittle.
In the photographic marketplace, platinum is the most highly esteemed of the non-silver processes. Platinum’s mystique derives partly from the fact that it is the most expensive non-silver process. Its cousin palladium used to cost much less than it does now. (Unfortunately palladium, among other uses, is now used in the catalytic converters of most cars.) However, at the time this is written, platinum solution still costs more than twice as much as palladium solution.
Historically, platinum prints were known for their subtle grays and palladium prints for their brown tones. This was in the days when platinum and palladium were developed in the traditional developer, potassium oxalate. Photographers often combined the two metals to achieve a range of tones that fell between the grays of platinum and the browns of palladium. Potassium oxalate is a more poisonous developer than ammonium citrate or sodium acetate developers which produce relatively cooler, grayer palladium prints that could be mistaken for platinum prints. Sometimes a palladium print is called a platinum print even if it doesn’t contain any of this metal. Also, some workers add a few drops of platinum salts to the palladium salts to ensure dark values that are black because of the tendency of pure palladium to solarize to brown — and/or to boost contrast with a certain kind of platinum salt. Such prints are often referred to as platinum prints.
Your choice of printing paper can make a great difference in the look of a final print. Palladium likes a slightly acidic surface on paper. An inexpensive wood pulp paper that has been buffered to combat its inherent acidity to the point of alkalinity gives a weak image in palladium. A soft cotton paper like BFK Rives soaks up the precious palladium solution and can pill leaving white flecks in the image.
Even a paper created for platinum/palladium, such as Arches Platine, which usually prints beautifully, can, on occasion, to deliver a palladium print that is either mottled or washed out. Photographer John Joyce used Platine for palladium prints for several years with excellent results but then for several months was plagued with mottled or pale prints as well as granulated (rather than smooth) tones. I was told by Kevin Sullivan of Bostick & Sullivan that some of these problems could have been the result of variations in humidity as well as subtle inconsistencies in the manufacturer’s sizing of individual mould-made sheets of Platine. I ordered some Crane’s Platinotype paper, both bright white and natural, which is manufactured in rolls rather than sheet by sheet and is thus more consistent, but we found that the surface of the Crane’s was easily abraded during coating and that it lacked sufficient wet strength to hang from clothespins without being cradled in a hammock of nylon screen. Fortunately, along with the Crane’s order Kevin sent samples of Bergger Cot320 paper that held up somewhat better during coating and processing, but with a new batch of Platine, John Joyce is back to using it. Other Pt/Pd printers have recommended Bienfang tracing paper, Opaline Parchment and Crescent paper.
More on Paper
If you are seduced by the sensuous qualities of Arches Platine paper, despite potential problems, and buy a 22˝ by 30˝ sheet, note which side of it has the right-reading ‘Arches Platine’ watermark. I used to think that you had to print on the right-reading side with its smooth plate finish, but Eric Kunsman, graduate student in Book Arts/Printmaking, got stronger, clearer renditions of his view camera negatives on the comparatively rough back of Platine. It may be that the infamous run of Platine described in the previous section had overly hard sizing on the smooth side that didn’t allow enough absorption of the palladium solution. But another factor could have been the alkalinity of the sizing, according to Kevin’s brother, Dana Sullivan. He said that some printers make the smooth side of Platine less alkaline by brushing 1% or 2% oxalic or citric acid on the image area and letting it dry before coating with the expensive palladium solution. Palladium printers who swore by double-coating the paper with slightly acidic palladium solution were simply making the paper less alkaline using a precious metal, a waste of money and resources. In any case, more recent batches of Platine have printed beautifully on the right-reading side.
It is important to handle whatever paper you decide to use without touching the image area on your paper. Greasy fingerprints can repel the palladium solution, leaving whitish fingerprints. Place your negative/light-resist on the paper just where you want your image to print and, using a pencil, lightly mark its corners. This will guide you in applying the palladium solution. Or, if you wish to coat only parts of the image area, lay the negative on the light table and, placing the paper on top of it, sketch lightly in pencil the shapes of areas you wish to coat.
Mixing Palladium Solution
Traditionally, three solutions are combined, drop by drop, in a clean vessel. (Glass or ceramic vessels work best though hard plastic containers can be used. Kara LaFleur discovered that Styrofoam containers do not work well.) Solution A (#1) contains light-sensitive ferric oxalate. Solution B (#2) is the same as Solution A except that a pinch of potassium chlorate, a volatile oxidizer which boosts contrast, has been added. Solution C (#3) contains the precious palladium salts. According to this method you control contrast by varying the ratio of Solution A to Solution B — with Solution C always the same. The chart below shows what we at UArts have found to be the amount of contrast rendered by various ratios of A to B in terms of graded silver paper and beneath those how the solution will print in terms of relative contrast:
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The smoothest, creamiest tones are rendered with the ‘very soft’ combination of 22 drops of A, no drops of B, and 24 drops of C, but to produce a print that isn’t muddy you need a negative with a great range of density. If you give a view camera negative twice the development time you’d give a negative intended for printing in silver you might have one suited for the ‘very soft’ mix. At the other end of the chart, to achieve the highest possible contrast, which isn’t much more than average contrast in silver printing, use 22 drops of B and no A solution. Try to avoid this combination because the potassium chlorate in B gives a grainy look to the print. ‘Contrasty’, obtained by combining 10 drops of A and 12 drops of B, gives a boost in contrast to images printed from average negatives that would be too thin to print in vandyke brown. But, and this is a big but, this ratio of solutions cannot compensate for thinner negatives that would need grade 3 or higher silver paper.
We order these 3 solutions already prepared in brown bottles from Bostick & Sullivan (see “Resources“). Since 24 drops of Solution C equals 11/2ml, approximately sixteen 8˝ x 10˝ prints, with enough excess for test strips, can be produced from a 25ml bottle. Be sure to use eyedroppers of the same design with each solution since the blunt-tipped kind gives a different size droplet from the more commonly used tapering eyedropper that is supplied by Bostick & Sullivan.
Sheer disposable gloves should be used when handling the little brown bottles of palladium chemistry. Heavy reusable gloves are too clumsy.
Combine the solutions in a clean vessel reserved for this purpose.
Sodium Chloroplatinate – Na2 20%
Although using the Bergger Cot320 paper solved the problems of mottling and pale printing, John Joyce still found granulation in midtones and highlights from negatives that he’d printed smoothly from in the past on the old batch of Platine that worked so well. It’s true that he was using the contrasty mix with 12 drops of B.
Dana Sullivan suggested a new/old way of printing that his father Richard had picked up on in his extensive readings of 19th century documents. This approach avoids the granularity associated with using potassium chloride to boost contrast and extends the contrast range of palladium. It involves using none of the B (#2) solution and substituting one or more drops of a form of an expensive platinum salt in solution called ‘sodium chloroplatinate’ for the palladium in Solution C (#3). Dana sent a sample bottle for us to try and the result was a perfect print for John Joyce after months of frustration. The black was especially deep and velvety since platinum keeps the palladium from solarizing (turning brown) in overexposed areas and there was not a trace of granulation. According to Dana, contrast can be extended well beyond what could be achieved with the ‘contrasty’ mix by substituting more drops of sodium chloroplatinate solution for drops of palladium solution C (#3).
Applying Palladium Solution
Haké brushes are often used for brushing on palladium solution. These wide flat brushes, usually from China, are made of white goat hair, wood and strong thread. There is no metal ferrule to interact with the chemicals and cause trouble. You can trim and bevel the brush to suit your needs. We have also found that sponge brushes work well, especially the narrow 1 or 2 inch size. At the beginning of a printing session your brush, either bristle or sponge, should be dipped in distilled water and then pressed between gloved fingers to remove excess water. The dampness of the brush will prevent some of the expensive palladium solution from being wasted. Witho Worms, a Dutch photographer who makes superb platinum/palladium prints, uses a DaVinci 5080 brush. This expensive brush has very fine nylon bristles. Witho presoaks the brush in distilled water and removes excess water before dipping into the palladium solution. He does this to prevent chemicals from getting into the brush — as well as to conserve. He says that a Richeson brush could also be used.
Apply the solution generously and as evenly as possible onto the paper. Forty-six drops will just cover an 11˝ by l4˝ area on a hard paper. An 8˝ by l0˝ area can be covered easily with 46 drops of palladium chemistry with enough left over for a test strip on the same kind of paper. Look at your freshly coated paper from an oblique angle to make sure its surface is covered with solution where you want it to be and isn’t puddling. Don’t worry if the coating isn’t perfectly even looking. Palladium is surprisingly forgiving in this respect. And if a hair or a particle ends up on the wet coated surface, just leave it there until the paper is dry and then blow it off with a hairdryer rather than disturbing the surface of the paper when it is wet.
The most economical way to apply palladium is with a specially designed coating rod (see ‘Edwards Engineered Products’ in “Resources“), which is essentially a tube with a handle. Tape the corners of the printing paper to a perfectly smooth surface when coating with a rod. Set the rod with its handle away from you at the top of the sheet and distribute the palladium solution along the edge of the rod with an eyedropper. Lift the rod, placing it behind the line of brown solution, and squeegee the liquid across the surface of the paper towards yourself; lift the rod and drag excess solution back across the image area away from yourself. Hopefully, two passes with the rod will coat the paper evenly but, if not, more passes can be attempted. Practice rod coating with cyanotype or vandyke solutions before trying it with palladium. Be sure to wash the tube thoroughly with water between different processes.
If you are using a thin, single-ply paper, tape it to a clean piece of glass or plexi so that it doesn’t move as you coat it. Brush on the palladium or use the rod applicator and then slip the glass or plastic support with the paper attached into the drying rack. This strategy prevents thin paper from curling in upon itself as it dries.
Or you may be working in a space where it is more practical to hang the coated paper from clothespins on a line. Make some arrangement when drying thin paper to ensure that it doesn’t curl in upon itself, perhaps by using extra clothespins.
Drying the Paper
Let the paper dry in darkness for about 10 minutes. This allows the solution to spread out evenly. Then, using the hairdryer on its lowest setting, dry the paper as evenly as possible, front and back. If you had taped the paper to a piece of glass or plexi, dry the front first and then un-tape one corner to gently blow warm air underneath the paper before taking all the tape off. Be careful not to blow the air towards yourself because microscopic bits of drying chemicals could be blown into your face and inadvertently inhaled. Do not touch the surface of the coated print to ascertain if it is dry. Instead feel the back of the print. If it is cool this means that the paper is still damp and requires more drying time. If the paper feels room temperature, another test to make sure that the paper is dry is to flex it. It will not flex easily if it is still damp because it will be ballooning out slightly on the coated side. Do not go overboard with the hairdryer on a palladium print since graininess can result. Kevin Sullivan has warned that very low humidity in heated rooms can also produce graininess.
Exposure: Test Strips or by Inspection
Exposure time for a palladium print is much less than for a cyanotype and may be about the same as for a vandyke with the following difference: the more bleach-like Solution B you use in the sensitizer, the longer your exposure time will be. (Those who print on multigrade silver paper with filters know that you have to increase exposure time when boosting contrast.)
A test strip is the surest way to determine an ideal exposure. It must be done on the same kind of paper as the final print and under the same conditions. A good test strip goes from underexposed to overexposed to reveal the entire range of possibilities. Each portion of the strip must capture parts of the image that have both highlight and shadow as well as mid-tones. Therefore you have to design a test strip intelligently before coating the paper. Place the negative on a light table and angle the test strip on top of it to capture pertinent information on each portion of the strip and then, with a straightedge and pencil, draw lines on either side of the negative to the edges of the test paper to guide the placement of masking material during exposures. Write the proposed exposure times between the penciled lines on both sides of the negative where they won’t be covered by palladium and will be visible to guide you during test exposures.
Test strip times vary with the light-resists’ densities and the light source. However, a hypothetical sequence of exposures for a continuous tone negative with dense highlights might be 10, 20, 40, 80 and 160 units on our platemaker with its particular calibration. This sequence is a doubling of each exposure rather than adding the same amount of exposure each time as you might do for a flat or relatively thin negative.
Tape one side of the negative to the test strip with two small pieces of clear tape so that the negative can be lifted from the print like turning the page of a book and printing-out can be checked without losing registration. (If you have a traditional split-back contact frame, there’s no need for tape since the negative can be held in place against the paper under the unloosened part of the back.)
Expose the entire test strip for 10 units. Then cover the portion that is marked ‘10 units’ with goldenrod (or some other mask that blocks actinic light) and give another 10 units to the remaining four parts of the test strip, bringing their exposure to 20 units. Cover the first and second portions of the strip and expose the rest of the strip for 20 units. Cover portions 1, 2 and 3 of the strip and expose the rest of it for 40 units bringing the total to 80 units. Finally, cover the portions 1-4 and give the fifth portion 80 units to bring the total to 160. Inspect the test strip while leaving the negative taped to it. If substantial printing-out has not occurred on the part that got 160 units, keep adding overall exposures with negative in place but with no masking until such printing-out does appear and revise your test strip times in the margins accordingly.
If you are not making a test strip but are instead printing by inspection, the common wisdom is to expose until there is the faintest indication of highlight detail rendered in rusty brown ferrous tones. (As in the vandyke brown process, the printed-out palladium image darkens considerably with development, but unlike vandyke it does not darken with drying, though it may dry down and seem to lose contrast.)
We used ammonium citrate as the developer for several years. It is expensive but is used over and over, and replenished with fresh developer to make up for volume that is lost by use. Only once in my experience has this developer expired from overuse. Although ammonium citrate developer is not in itself poisonous (unlike traditional potassium oxalate developer which is quite toxic to begin with), it should be used under a fume hood or outdoors because it becomes contaminated with ferric oxalate that leaches off prints developed in it and fumes from the ferric oxalate can give you quite a headache, something I know from experience.
Over the summer John Joyce tried potassium oxalate developer at the suggestion of Ernestine Ruben to see if he could get rid of granulation in the skies of his landscapes. It worked for him in combination with the sodium chloroplatinate (Na2 20%) and the Bergger Cot320 and he can accept the browner rendition of a print that comes with this developer. Beginning in Fall ‘03 we’ve used the potassium oxalate in the fume hood with excellent results.
Slip your exposed test strip or print face up into whichever developer you use and make sure that the entire surface of the paper is covered with developer quickly. This will help to avoid ‘lap’ marks on your print. Development is almost instantaneous and need not continue longer than one minute with continuous agitation. The palladium salts lying in contact with the ferrous salts will reduce to form the image.
If you can’t seem to avoid ‘lap’ marks on your print, you might try diluting the developer with water. Dana Sullivan put forth this idea but did not give suggestions about how much to dilute it.
Before proceeding to the clearing baths, submerge, agitate and flip the print in a tray of plain water, allowing unexposed ferric and palladium salts to slough off the paper and sink to the bottom before proceeding to the clearing baths. Change the water in this tray when it gets murky.
To have a stable print of pure palladium, it is critical to remove the iron salts that initially formed your image. If you don’t, these salts can darken later in highlights as sometimes occurs with vandyke brown prints. In the past, hydrochloric acid diluted in water was used to literally etch away the iron salts, but such a strong acid tends to make paper fiber short and brittle. It seemed like an advance to switch to less hazardous, gentler citric acid which we used for a number of years. Over the past several years, however, we have been using EDTA (ethylenediamine tetra-acetic acid) to remove iron salts from the palladium print. EDTA functions not as an acid but rather as a chelating agent that hooks up with the iron molecules and gently removes them from the paper.
Three trays of clearing baths should be prepared. Each of the three trays contains approximately 4 tablespoons of EDTA dissolved in 60 oz. of slightly warm tap water. The powdered EDTA dissolves quickly with a little stirring and dissolves even faster if the water is poured onto the powder heaped up in the tray. Take your newly developed print from the rinse tray to tray #1 and agitate it gently for 5 minutes, much of the time face down. (You can make sure that there are no air bubbles trapped under the face-down print by raking the surface of liquid with the edge of the print to break any visible bubbles and then lowering the print holding it by diagonally opposing corners so that the center of the print touches the liquid first and air bubbles can escape. You will not like what happens where air bubbles are trapped: i.e., brown circles of uncleared sensitizer that are hard to get rid of.) The tan-rust highlights begin to whiten as the iron salts are removed and the tone of the image starts to cool. Move the print to tray #2 and agitate for another 5 minutes. Repeat with tray #3.
Residual yellow in highlights can be removed in a bath of sodium sulfite. The concentration of sodium sulfite is not critical since you will leave the print in it until the yellow has gone away. Witho Worms mixes sodium sulfite with EDTA. He combines 30 grams of sodium sulfite with 60 grams EDTA in 4 liters (1 gallon) of water. We now add ≈ 2 tablespoons of sodium sulfite to ≈ 4 tablespoons of EDTA in each tray with good results. Finally, wash the print by itself in tap water with the tray siphon running at a moderate speed for a bare minimum of five minutes with frequent flipping, and preferably for longer when we are not in a drought.
When the solution in tray #1 becomes cloudy after a few prints have passed through it, discard the solution and shift tray #2 into #1’s position. Tray #3 moves into #2’s position. In the former tray #1, mix EDTA and sodium sulfite in fresh tap water and place it where #3 was. This way the baths will remain most effective and the least contaminated tray will always be the last clearing bath. At the end of your printing session save the contents of the third clearing bath to use in tray #1 in your next printing session — unless it has been used so much that it is discolored.
Rescuing Palladium Prints
An over-exposed palladium print cannot be bleached back to an acceptable tonal range but, if you are not a purist, you could draw or paint or print on top of it in light, opaque (or semi-opaque) colors to bring back highlights.
If your palladium print is underexposed, you can strengthen it by printing over it again with another coat of palladium, or a layer of cyanotype or vandyke. Cyanotype works especially well to strengthen shadow areas. Its blue coolness contrasts in a satisfying way with the warm gray of the palladium and deepens shadows to a dark pewter color. The cyanotype layer can be bleached to increase contrast without affecting the underlying palladium. Of course you might have registration problems if the paper wasn’t preshrunk before you coated it with palladium — people generally don’t preshrink paper when they intend to print a single layer of palladium — but on the other hand, paper printed in palladium shrinks less than paper printed upon in gum or even cyanotype or vandyke (for reasons I do not know). Unfortunately we have found that when we print a second layer in any process using the same half-tone negative from the Scitex imagesetter, moiré patterns tend to emerge due to the rows of halftone shapes getting the slightest amount off register. Fortunately, this does not happen with inkjet desktop negatives which are printed in random dots. It can be avoided with halftone negatives by creating a second negative with a different angle to the halftone dots as happens if you go into duotone mode. The shrinkage issue as well as the expense of a second coat of palladium can be gotten around by exposing the duotone separations sequentially onto the same coating of palladium solution. No halftone pattern can be discerned and the print has a velvety richness that rivals the best prints from view camera negatives.
If you print in gum on top of palladium you face sizing issues that are described in the following “Gum Bichromate” chapter, but gum was printed on top of platinum with great success by Edward Steichen. When BFK is sized with gelatin, hardened in formaldehyde and printed upon in palladium, ugly yellow highlights result. Steichen may have gotten BFK to work for him by printing platinum on preshrunk BFK which is less fluffy (thus less prone to pilling), and then sizing the paper. Yellow highlights also appear when palladium is printed on watercolor papers that are pre-sized with hardened gelatin. This yellowing may not appear on paper that has been sized with gelatin but not hardened with formaldehyde which is our new preferred way of working. This is something that should be tried and will be reported on in the next revision of this manual.
I used to warn that printing in gum on top of palladium on Arches Platine is disappointing because the surface that comes sized for printing in platinum/palladium doesn’t have sufficient tooth to hold gum emulsion yet stains with freckles of pigment. The part about the freckles is true but it also seemed to me that the smooth surface of Platine would not take gelatin sizing. Once again I have been pleasantly surprised by students who, after printing a layer of palladium, insisted on sizing Platine with two layers of gelatin, and got good results printing in gum over palladium. Special student Michele Robins has now done this successfully many times.