Jean-Claude Mougin shares his text on Palladium in 3 parts, The palladium and platinum salts, Part 1: The Object, Part 2: The Technique (this article) and The palladium and platinum salts, Part 3: The Recipes and Bibliography (coming soon).
Read the previous article The palladium and platinum salts, Part 1: The Object
Note from the author: the ✌, sign refers to a personal interpretation of the technique discussed.
1. Historical Background
1803. Wollaston discovers palladium.
1886. Döbereiner realizes the reduction of platinum chloride by light. 1831. The same chemist discovers the light sensitivity of ferric oxalate.
1844. Robert Hunt, in his work ” Researches on Light ” reports on his experiments with platinum.
Hunt covered a sheet of paper with a mixture of ferric oxalate and platinum chloride which were darkening when exposed to light. But he was not able to discover the principle of its processing for permanency.
1873. William Willis, son of a famous English engraver, works out the process.
Three patents for a platinotype process were successively granted to him: British Patents of June 5th, 1873; August 20th, 1878 and August 15th, 1880.
1880. Willis founded the Platinotype Company marketing his platinum paper in England. The Willis & Clements company from Philadelphia distributes it in the United States. From 1911 onwards, those two companies are selling up to 15 types of papers.
1882. Giuseppe Pizzighelli and Arthur Baron Hübl, two Austrian Army officers, describe a manual method enabling photographers to prepare their own paper. Their dissertation incurred the wrath of the Platinotype Company which will try to disconsider their formulae. Il will be translated successively into English and French and even today, it is still considered a reference.
1883. Creation of the Platino-Union in Austria. Platinum papers platinums are subsequently marketed by Ilford Company and Hesekiel in England, Gevaert in Belgium, Hesekiel Jacoby in Germany, American Aristotype Co., Ansco and Kodak in the United States.
Nevertheless, the platinotype wasn’t quite successful in France where the photographers used to prefer the carbon, Artigue and Fresson processes.
Famous photographers adopted the platinotype process, such as Frederik Evans, Emerson, Stieglitz, Steichen, Coburn, Strand, Weston, Tina Modetti, and Manuel Álvarez-Bravo.
1914. From this date, the platinum rates are skyrocketing, until reaching five times the value of gold, which results in a gradually decreasing demand for these papers.
1916. The Platinotype Company introduces a cheaper palladium paper, the “palladiotype”, as well as a silver-platinum based paper.
1916. Kodak stops the manufacturing platinum paper.
1937. No platinum paper is imported in the United States anymore. 1941. Production is stopped in Great Britain.
1990. Creation of the Palladio Company in the United States, marketing a paper sensitized with platinum related metals.
2. The Revival of the Process
Over recent years, the platinum and palladium processes are reviving, for the following reasons:
- The disappearing of quality bromide and chlorobromide papers, replaced by resin coated papers of questionable aesthetic quality.
- The arrival of photography on the art market. Due to its permanence qualities, its matt appearance similar to that of engravings, its unrivaled physical presence, its “tactile” aspect, its rendering of an extremely broad range of shades, and a big variety of colors, the platinum-palladium image increasingly becomes essential as the process of reference and is considered a significant bonus by galleries and collectors.
- The simplicity and the flexibility of the process. It is accessible to any photographer having good darkroom skills. It suits an important range of supports, of papers with various textures. It allows producing images in a broad range of contrasts and colors.
Luis Nadeau: History and Practice of Platinum Printing
3. Summary Description
- Palladium and platinum salts are not photosensitive, and therefore have to be combined with ferric oxalate which is light-sensitive.
- The mixture is coated with a brush on a good quality paper. This can be done under tungsten light without any problem, as the ferric oxalate is sensitive only to ultraviolet rays.
- After drying, the negative is contact printed on paper under the sun or under a U.V. lamp.
- The action of the light transforms the ferric oxalate in ferrous oxalate.
- After exposure, the image is developed in a bath of ammonium citrate or potassium oxalate. These substances dissolve the ferrous salts and reduce palladium or platinum salts to a metallic state. The image, hardly visible after exposure, appears almost immediately when immersed into the developing bath.
- The ferrous salts remaining in the paper and giving it a yellow stain are dissolved in a bath of diluted hydrochloric, oxalic or citric acid.
- The image is finally washed in order to eliminate all acid substances and dried. It is now entirely formed by palladium or by platinum which are stable metals. The permanence of such an image, therefore, equals that of its support.
- The process has nevertheless a limitation. It is not possible to print an enlarged image. Unless using large format negatives, negatives at the size of the final print have to be made in the darkroom.
The formulae
4. The Negative
4.1 Large format negatives
For platinum – palladium printing, it is necessary to start from a negative having the size of the final positive print. It would, therefore, be ideal to use a large format camera, providing 4″x5″, 5″x7″ or 8″x10″ negatives for instance.
When doing so, it is advisable to process the film in order to get a contrasty negative, necessary to provide details in the highlights, and dense enough to preserve details in the shadows. For an optimal rendering of the tonal range in a subject, the negative density range from shadows to highlights should be somewhere between 1.3 and 1.5. This corresponds in the Zone System to N+1 or N+2 negatives. A N+1 negative has a density of about 1.3 and is printed on grade 1 paper. A N+2 negative has a density of 1.5 and is printed on grade 0 paper.
4.2 Measuring the contrast of a negative
Normally, a densitometer should be used, but this, unfortunately, is an extremely expensive device. A more affordable means is to use a step wedge such as the “Kodak Step Tablet #2” or the “Agfatrans”, the latter being much less expensive.
The Agfatrans, Kodak, or Stouffer step wedges are film strips having a series (usually 21) of progressively and uniformly darker steps, the difference of density between two steps being 0.15. Their size usually is around 1″or 1/2″ x 5″ (13 or 25 x 125 mm); Stouffer also proposes different sizes, such as 4″x5″.
In order to determine the density range that a negative should have for a specific type of emulsion, the step wedge has to be contact printed on this emulsion. After the processing and drying of the sample, the density of the first black step which cannot be differentiated from the previous one is noted. Next, the density of the last step showing a difference with pure white is noted also. The difference between both densities indicates the actual density range.
To determine the contrast of a given negative, it has to be contact printed on a sheet of multigrade paper, side by side with the step wedge, adapting the exposure until a well-balanced print of the negative is obtained. Its density range can then be estimated from the step wedge, using the same method as above.
4.3 Various methods for making an enlarged negative
4.3.1 Inversion during the processing of the enlarged positive
- Don Pardoe in “Lumen IV” 1984
- Roger Kockaerts: Procédés Nobles En Photographie
4.3.2 Enlarging the negative to obtain a positive, and finally get a negative of the required size by contact or enlargement
- Roger Kockaerts: op. cit.
The author gives directions for the processing of three emulsions:
- Gevatone N31p
- Ilford Ortho
- Kodak Commercial Film
Those films do not exist anymore. It is possible to use Ilford FP4 sheet film in complete darkness. The same film has an ortho version that can be handled under a red safelight. Maco Genius Print Film is a continuous tone film, which is also marketed under various brands, such as Bergger or Freestyle.
5. The Negative: My Method ✌
5.1 Equipment & materials used
- Beseler 45V-XL enlarger w/ dichro 45S color head, Nikon 5,6 /135 mm lens
- Ilford Multigrade IV RC MGD 25 M satin paper
- Ilford FP4 sheet film
- Ilford PQ Universal developer
- A rotary paper processor
- N+1 developed 2.4″x2.4″ negatives, for printing on grade 2 paper (or without a filter for multigrade) under a diffuser enlarger
5.2 The making of a reference print
Make a print from a chosen negative as usual, with all the corrections you consider useful.
Process in PQ 1+9, 1 mn 15, at 20°C. This print will be used as a reference. Keep notes on the opening of the f-stop and time of exposure, for instance, 10 seconds at f16.
5.3 The making of a 4″x5″ positive
The positive should be dense and low contrast; more specifically, it should not have any fully transparent area.
On no account, it has to look like a normal slide. The highlights, last clear zone showing some texture, should have a density of approximately 0.95 (step 7 of the Stouffer wedge). And the shadows, the darkest zone, a density of 2.15 (step 15 of the Stouffer wedge).
5.3.1 Exposure
Put in the easel under the enlarger, instead of a variable contrast paper but under same conditions, a 4″x5″ FP4 sheet film, the clearest part above. This has to be done in total darkness.
Reduce exposure to 1/4th of the one used for the paper print, for instance, 5 seconds at f11 for the example above. Add 200 CY and 200 YE filters, and apply the same reduction to all correction exposures, if there were any.
5.3.2 Processing
Process the 4″x5″ sheet film in a rotary processor, such as the Jobo.
- Pour the developer in the tank and start rotation.
- Stop the development after 12 mn by a water rinse
- Fix 1 min. in Hypam 1+4 with continuous agitation
- Wash, drain, dry
5.4. The making of the final 8″x8″ or 8″x10″ negative
Set the height of the enlarger so that the negative carrier is at H 303 on the scale. Enlarge the 4″x5″ negative, using T/2 time. The negative should look rather dense with details in the shadows and a density range between 1.7 and 1.9.
-> This protocol is given as a rough guide and should be adapted according to your own experiments, to take into account possible equipment differences.
6. The Paper
6.1 Handmade, machine made
The appearance and the archival qualities of a palladium print depend heavily on the choice of the paper used as emulsion support.
There are two paper types: handmade or machine made.
The first usually is 100 % rag, made from a pulp (often cotton rags), using a frame, or mould. The mould is dipped into the wet pulp, shaken to distribute the fibers and drained of its excess water. The newly formed sheet may be hot pressed or cold pressed, to obtain a smooth or more or less rough surface. It finally is dried against blankets or (hot) air dried
The second is made on very rapid running machines producing consistent quantities of sheets or rolls. It usually is made from sulphite pulp, containing bleached wood cellulose. It may contain a variable proportion of cotton rags. A paper with high cotton content has a more or less pronounced ivory tint. An extra white paper is generally of low quality.
6.2 Sides
There is a difference between the two sides of a sheet of art paper. The reverse side sometimes keeps a slight texture from the felt or cylinder against which it was pressed. The front side has a smoother surface and a more homogeneous structure. This difference can be noticed visually and is even more recognizable when the sheet is held to the light.
Some papers have watermarks. Its design is imprinted on the back side of the sheet, which explains that the trademark appears inverted when the sheet is held to the light. Other papers have an embossed mark which allows identifying the front side.
6.3 Sizing
Sizing a paper improves its surface; substances are added to provide resistance to the absorption of moisture or to eliminate ink feathering and bleed through. These substances can be gelatin, starch or synthetic.
Calendered paper was glazed or smoothed by passing between rollers to get an extremely glossy and smooth surface. This is the case for Bristol papers for instance, which are not adequate for platinum-palladium printing.
6.4 pH – can be measured with a pH pen (Atlantis)
The current preservation standards for papers, as well as environment protection requirements, induced changes in paper manufacturing. Basal binders were substituted for the acid ones, and sometimes papers are buffered with alkaline substances such as sodium carbonate.
These changes are a source of almost insoluble problems. The sensitizing substances being acid react with the basal support and lead to disastrous results, in particular with platinum salts which became practically unusable with modern papers. It is possible to acidify the paper by soaking it for 10 to 20 minutes in a 5% oxalic acid solution, and finally rinsing and drying it. (Dick Arentz gives more detailed information for specific papers). A double sizing layer can help also.
6.5 Which paper?
Preference should be given to a paper having good physical qualities and a high rag content as well as a neutral or slightly acid pH. The paper has indeed to resist the treatments as well as the repeated or long soakings inherent to the process and to guarantee a long lifespan to the print.
The choice can be influenced by aesthetic criteria. The tint of the paper influences the final color of the print. Its sizing also: starch gives warmer tones, gelatin colder.
The smoother papers give sharper images, while textured papers, especially watercolor papers with “torchon” surfaces rather enhance a pictorialist character. Usually, rag papers for engraving do not suit. Their sizing is not sufficient and their alkalinity is too high.
Watercolor papers generally work well, at least when their chemical characteristics are adequate. Contrast and sharpness might be low, but the “tactile” aspect of the prints made on such papers is sometimes looked for.
The so-called technical papers, when they are of good quality, give generally very good results when maximum contrast is what you are looking for. The blacks are deeper and the sharpness of the image is good. Today, however, either they have disappeared, or they are unusable because of their alkalinity.
6.6 Usable papers
distributed by Bostick & Sullivan
- Cranes Kid Finish has become unusable
- Weston Diploma
- Stonehenge (not tested)
watercolor papers
- Arches satin grain – pads or sheets (has to be acidified)
- Arches Platine, currently the best paper
- Bergger COT-320, very similar to Arches Platine
- Rives BFK, has to be sized and acidified
- Fabriano Artistico, has to be acidified
japanese papers
- japanese papers usually have an acid pH, but are unfortunately quite absorbent and have therefore to be sized.
writing papers
- Currently, all writing papers are alkaline. It is possible to find adequate old papers on Ebay – ream papers or correspondence papers.
papers from the Ruscombe Mill, made in accordance with Mike Ware’s advice
- Buxton paper, excellent but with a rough texture.
- A new Herschel paper is proposed, which is a linen paper instead of cotton rag; it is said to be smoother.
7. The Sensitizing Solutions
7.1 Required equipment/products
- a scale with 0,1gr resolution
- 3 brown bottles of 125 cc or more
- ferric oxalate from Bostick and Sullivan
or the ferric oxalate made according to the technique given in my “small treatise on iron salts” (recipe 3, see further) - potassium chlorate
and/or a 3 % solution of hydrogen peroxide (10-volume)
and/or a 4 % solution of potassium dichromate - sodium chloropalladite
or palladium chloride + sodium chloride - potassium chloroplatinite
7.2 The classic method
The sensitizing solution is prepared from three primary solutions:
- A solution of ferric oxalate.
- A solution of ferric oxalate supplemented with an oxidizing substance the purpose of which is to increase the emulsion’s contrast. The classic formulae use potassium chlorate.
- A palladium or platinum salt solution.
These solutions have to be prepared with the usual precautions.
WARNING:
Use only glass or plastic containers. Any contact with metal must be banned. Label the solutions and keep them in a cool, dark place.
7.2.1 Preparation of solution #1
- distilled water at 50°C ……………………. 55cc
- oxalic acid ………………………………………. 1gr
- ferric oxalate ………………………………….. 15gr
This is a 27 % solution of ferric oxalate. This percentage is not critical. Literature mentions dilutions ranging from 20 to 27 %. These differences have no influence on the quality of the image.
Dissolving is not easy; it requires constant agitation and patience. Raising the temperature beyond 50 °C, but below boiling point, will help.
7.2.2 Preparation of #2 palladium solution
- distilled water at 38°C ……………………. 55,0cc
- oxalic acid ……………………………………….. 1,0gr
- ferric oxalate …………………………………. 15,0gr
- potassium chlorate ……………………….. 0,3gr
7.2.3 Preparation of #3 platinum solution
- distilled water at 38°C ……………………. 50cc
- potassium chloroplatinite ……………… 10gr
7.2.4 Preparation of #3a palladium solution
- distilled water at 38°C ……………………. 60cc
- sodium chloropalladite ………………….. 9gr
7.2.5 Preparation of #3b palladium solution
- distilled water at 38°C ……………………. 40,0cc
- sodium chloride ………………………………. 3,5gr
- palladium chloride …………………………. 5,0gr
7.2.6 Fine-tuning for contrast
The print contrast is controlled by adapting the proportions of #1 and #2 solutions according to following formulae:
very contrasty negative: density range 1.8
- solution #1 ………………………… 24 drops
- solution #2 ………………………… 0 drops
- solution #3 ………………………… 24 drops
contrasty negative: density range 1.5
- solution #1 ………………………… 20 drops
- solution #2 ………………………… 4 drops
- solution #3 ………………………… 24 drops
medium contrast negative: density range 1.35
- solution #1 ………………………… 16 drops
- solution #2 ………………………… 8 drops
- solution #3 ………………………… 24 drops
moderate contrast negative: density range 1.2
- solution #1 ………………………… 12 drops
- solution #2 ………………………… 12 drops
- solution #3 ………………………… 24 drops
low contrast negative: density range 1.05
- solution #1 ………………………… 0 drops
- solution #2 ………………………… 24 drops
- solution #3 ………………………… 24 drops
7.3 Other methods
7.3.1. Personal method #1 ✌
While solution #1 keeps its qualities for several months, this is not the case for solution #2. The latter should be discarded after a few days, unless you are prepared to accept a significant loss in quality, with decreasing contrast and an indelible yellow veil.
It, therefore, is preferable to prepare this solution in small quantities and to increase its potassium chlorate concentration.
Solution #1
- distilled water at 50°C ……………………. 55cc
- oxalic acid ………………………………………. 1gr
- ferric oxalate (*) ………………………………….. 15gr
(*): use homemade, following recipe 3 in my “small treatise on iron salts”
Solution #2
- solution #1 (see above) ……………………. 2,5cc
- potassium chlorate ………………………….. 0,1gr
Prepare solution #2 the day before use; discard after 2-3 days
For a maximal tone range, it is advised to avoid too soft or contrasty negatives. This allows to restrict ourselves to only the three following formulae:
contrasty negative: density range 1.5
- solution #1 ………………………… 23 drops
- solution #2 ………………………… 1 drops
- solution #3 ………………………… 24 drops
medium contrast negative: density range 1.35
- solution #1 ………………………… 22 drops
- solution #2 ………………………… 2 drops
- solution #3 ………………………… 24 drops
moderate contrast negative: density range 1.2
- solution #1 ………………………… 21 drops
- solution #2 ………………………… 3 drops
- solution #3 ………………………… 24 drops
7.3.1. Personal method #2 ✌
With this more convenient method the oxidizer is introduced in the developer – and not, as previously, in the emulsion.
This allows saving some potassium chlorate which is an unstable product, dangerous to manipulate, and difficult to weigh.
Two oxidizers were tested: a 3% hydrogen peroxide solution, and a 4 % potassium dichromate solution.
Tests completed on Arches Platine paper
very contrasty negative: density range 1.95
- potassium oxalate …………….. 24
- cc oxidizer ……………………………… 0 cc
contrasty negative: density range 1.8
- ammonium citrate …………… 100cc
- oxidizer ……………………………. 0 cc
- potassium oxalate …………… 100 cc
- oxidizer ……………………………. 1 cc
medium contrast negative: density range 1.35
- ammonium citrate …………… 100,0cc
- oxidizer ……………………………. 0,5 cc
- potassium oxalate …………… 100,0 cc
- oxidizer ……………………………. 1,0 cc
moderate contrast negative: density range 1.20
- ammonium citrate …………… 100cc
- oxidizer ……………………………. 1cc
- potassium oxalate …………… 100cc
- oxidizer ……………………………. 2cc
low contrast negative: density range 1.05
- ammonium citrate …………… 100cc
- oxidizer ……………………………. 2cc
- potassium oxalate …………… 100cc
- oxidizer ……………………………. 4cc
For warm tones, process in citrate developer (see below).
Sodium citrate, which is my preferred developer, can be used at t° as low as 7°C. Contrast increases and tones are colder.
8. Sensitizing the Paper
8.1 Required equipment
- one of the papers selected under 6.6
- the prepared ferric oxalate, palladium & oxidizer solutions
- in each 125cc bottle, a 1ml syringe without its tip: 1 ml BD PLASTIPAK or similar – they will be used as measuring instrument or dropper and stay permanently with their respective bottles
- cover the syringe’s graduations with tape to avoid them to be dissolved in the solutions
- a graduated set square and a fine pencil (0.5)
- various types of tape: Scotch, Tesa Post-it, microporous bandages
- 1 brush similar to Pébéo Orion brush series 9451 (flat brushes made of yellow polyamide fiber with very fine tips, stainless steel ferrule, and a long handle.)
- cover metallic ferrule with tape to avoid every metal-emulsion contact
- a plastic or porcelain cup
- a lab wash bottle filled with distilled or mineral (Volvic..) water
- kitchen roll
8.2 Define the borders of the area to be sensitized
Determine an area to be sensitized corresponding to the size of the negative. If you wish to have straight edges, mark them with pressure- sensitive adhesive tape:
- with Scotch Tape for the “technical” papers
- with Scotch or Tesa tape, without excessive pressure, for Arches or watercolor papers
8.3 Prepare the iron-palladium mixture
- measure the surface
- multiply this surface expressed in cm² by 4, and divide the result by 1000. The result corresponds to the quantity of emulsion (in cc) sufficient to cover the delimitated surface:
For instance, in case of a 150 cm² area 150 x 4 = 600 : 1000 = 0,6
corresponding to 0,3 cc of ferric oxalate and 0,3 cc of palladium - Syringes should be preferred to droppers for measuring those quantities, as droppers give rather unpredictable results.
- A drop usually is equivalent to 0,05 cc, which means that about 10 drops are needed for 150 cm2.
- Take the ferric oxalate and the palladium from their bottles, mix both liquids in the cup and replace the syringes, without rinsing, in their respective bottles. (It is possible to keep the iron-palladium mixture in one same bottle for one or two weeks).
8.4 Sensitizing the paper
- this stage can be completed under dim tungsten light
- moisten thoroughly the brush with the wash bottle
- wipe it thoroughly with kitchen roll to get it hardly damp
- dip the tip of the brush in the emulsion
- spread the emulsion from an edge of the paper, without hurry, crossing the strokes
- holding the brush flat, equalize very delicately
- when finished, rinse the brush and cup with the washing bottle
8.5 Sensitizing timing
- This time is extremely important, especially with technical papers, and has to be controlled precisely.
- Technical papers are very hard, and the emulsion penetrates the paper quite slowly. This is, in fact, a quality; the emulsion remains on the surface and does not “sink” too much into the paper, which is why these papers give deep blacks and a high resolution. The risk, however, is that the emulsion doesn’t go at all into the paper and could be washed away by the developer during the processing. We can then see black streaks coming off the image.
- Arches Platine requires to be sensitized for 3 minutes. After being sensitized, the paper shouldn’t show any shine. Leaving it for 5 minutes in the dark allows the emulsion to sink into the paper.
9. Drying the Paper
9.1 Required equipment
- A hair dryer of the 1000w type, with an intermediate heat setting. Avoid too powerful dryers.
Drying procedure
This is an important stage, which has to be completed very carefully.
The drying has to be done from the backside, holding the hairdryer a few cm. away, moving it smoothly, with the heat set on the intermediate position.
If the coating comes off in the developer, the procedure has to be adapted. In that case, after the sensitizing, the paper should be left for 5 minutes, face up and in the dark (an empty box can be used for this purpose). After this, the print can be dried from the backside.
- The heat should not exceed 40°C
- 2 min. drying for the front side, 1 min. for the backside
- Dick Arentz recommends to use a damp paper, as for Ziatypes. The humidity fosters the printing out of the blacks, and shortens the necessary exposure; this will, however, cause a self-masking and might prevent from reaching maximum blacks. I, therefore, recommend the “dry” method which allows obtaining maximum Dmax, with darkening continuing deep into the paper fibers for as long as 2 hours of exposure. Longer exposures would cause solarization; this might have an aesthetic effect, which would however hardly be reproducible.
10. Exposure
10.1 required equipment
- Ultraviolet printing light:
✔ HID lamps (metal halide / mercury vapor), such as HPR 125 w Philips
✔ a light box with U.V. tubes - The HID lamps are twice as actinic at 32cm, than the U.V. tubes at 5cm. But the light box is more convenient as it produces less heat and easily allows for even illumination of negatives larger than 5″x7″.
- Printing frame, Paterson or other
- Sunglasses, to protect your eyes from ultraviolet rays
- Timing device
10.2 Exposure
The palladium emulsion is sensitive only to ultraviolet light. The print could be exposed to the sun, but using U.V. printing lights is more convenient.
- position the printing frame with a negative/palladium paper sandwich:
✔ at 5cm from the U.V. tubes
✔ at 30cm from the HID lamp; the lamp requires 5 minutes to reach full intensity - Exposure may vary from 10 to 30 min.
- Light sensitivity depends also on the type of paper.
It has to be noted that the exposure is influenced by the type of paper and sizing. “Cold”, gelatin-sized papers, such as Arches, need exposures twice as long as for starch-sized papers. (see also paragraph 6.6).
10.3 Exposure timing
Proceed as usual, making test strips and after processing and drying of the sample, determining the exposure time and possible corrections.
Those using a densitometer and the Zone System, might have a look at my “Z/S” document (in French), downloadable for free from www.platine-palladium.com
- First test: unexposed but processed negative; find Standard Print Time (PST) giving visually maximum black (usually between 15 and 30 minutes).
- Make a test with a 4″x5″ Stouffer step wedge; find zone1, film speed and tonal range for a given processing.
- Measuring with a densitometer a given negative, find how much it is over- or underexposed, comparing it to the Stouffer step wedge (avoid underexposed negatives if possible); it is possible to find the printing time without further testing by adapting the SPT according to the indications of the table below.
between two negatives, one being the reference; if this difference is positive (your negative is denser
than the reference), the column “+” shows the factor to be applied to the reference’s exposure in order
to find the exposure giving a final print with similar values to those of the reference print. If the gap is
smaller (your negative is clearer), the factor of the column “-” has to be used.
<strongExample: Reference negative = a Stouffer step wedge, from which the best possible print was made,
based on the necessary test strips. Let’s suppose that the final print required an exposure of 15
minutes. Considering a specific step – step 9 for example – we see that this step has a certain density,
say 1.33. In the print made from the step wedge, this density corresponds to a given grey value, close
to the neutral grey of the “Kodak Gray Card”.
Take now your negative.
Identify a part of the negative which you would like to see in neutral grey on your final print.
Measuring this part of the negative, you get a density value – let’s say 1.63. The difference of your
negative’s density with the one of the step wedge is thus: 1.63 – 1.33 = 0.3 (denser) which corresponds
to a correction factor of 2. You will have to expose your print for 15minx2=30min. The same kind of
calculation can be made if you want to get a denser/lighter print.
10.4 Corrections
It is possible to apply some corrections by increasing or reducing the exposure on certain areas of the print, but these actions can sometimes be quite time-consuming.
It is easier to modify the exposure when using HID lamps instead of a lightbox, as exposure time can be reduced significantly by bringing the lamp closer to the printing frame (the tubes banks being already very close leave less leeway). Remember that the light intensity is inversely proportional to the square of the distance from the light source.
11. Processing
The process consists in precipitating metallic palladium with appropriate salts, mainly potassium oxalate, ammonium citrate, sodium citrate, and sodium acetate.
11.1 The traditional method
With this method, the palladium print is immersed after exposure in a slightly acidified solution of potassium oxalate. The image appears almost immediately. Agitate for one or two minutes.
11.2 Developer formulae
- potassium oxalate ……………………….. 500 gr
- water, at 50°C or more ……………………….. 1500 cc
- maintain pH at ……………………….. 5.5 / 6
cold bath (not tested)
- potassium oxalate ……………………….. 500 gr
- monobasic potassium phosphate ………. 60 gr
- water, at 50°C or more ……………………….. 1500 cc
- maintain pH at ……………………….. 5.5 / 6
Baths to be used at temperatures between 15°C and 20°C
- ammonium citrate ……………………….. 500 gr
- water, at 50°C or more ……………………….. 1500 cc
- maintain pH at ……………………….. 5.5 / 6
- sodium citrate ……………………….. 500 gr
- water, at 50°C or more ……………………….. 1500 cc
- maintain pH at ……………………….. 5.5 / 6
Homebrewers: see chapter III Recipes, §3, 4 and 5
The literature insists on the fact that the developer is considered inexhaustible and can be used infinitely; it is even said that he would improve in time provided the pH is maintained at 5.5.
11.3 My personal method ✌
My experience contradicts these facts. Indeed the developer gets loaded with particles of palladium, but also of ferrous oxalate which in strong concentration eventually veils the print in an indelible way. It, therefore, is preferable to use one- shot baths, which certainly is more expensive, but has the merit to give quality results. The inconvenience of the price is reduced when you homebrew your developers. Homebrewers: see chapter III Recipes, §4, 5 and 6
Processing procedure
- use trays with a flat bottom, slightly larger than the print to be processed
- prepare 50 cc of developer for a print up to 8″X10″. Check the pH, if necessary; it should be kept between 5 and 6.
- when working at high temperature, add the oxidizer necessary for contrast at the last moment, and agitate well to homogenize the solution
- place the print on the bottom of the tray
- pour rapidly the developer on the print, agitate regularly for 1 min. Timing is not critical and doesn’t cause any increase of contrast
- clarify
11.4 Temperature & contrast
Palladium prints usually are processed at room temperature. Platinum prints require high temperatures, between 50°C and 100°C, otherwise, they will be grainy.
Contrast varies with temperature – increasing at lower temperatures, decreasing when temperatures get higher. A palladium print can be processed from as low as 7°C up to 100°C with sodium citrate.
11.5 Temperature & color
Temperature influences significantly the color of palladium prints – the colder the developer (to as low as 7°C), the colder the tone of the print; the warmer the developer (up to 100°C), the warmer the print tone.
This is less true for platinum prints, which are naturally cold-toned and actually appreciated for that very reason.
On the other hand, platinum prints require a high temperature, well over 50°C and up to 100°C, if order to avoid grainy prints. If a very warm developer is used, the oxidizer has to be added at the last moment, as he will be neutralized by the heat.
11.6 Oxidizer & color: Palladium prints on Arches Platine
- The coldest developer is sodium citrate at 7°C with potassium dichromate.
- Ammonium citrate with hydrogen peroxide is warmer.
- Potassium oxalate with potassium dichromate gives warm tones, and even more so hydrogen peroxide.
- It is important to note that color changes can vary significantly, depending on the brand – and even the batch – of the paper being used.
11.7 pH of the developers
For platinum as well as for palladium prints, it is imperative to have an acid pH (pH 5-6); with a basal pH, the clearing of the paper will indeed be impossible.
11.8 Platinum or Palladium prints?
- It becomes increasingly difficult to make platinum prints, due to the excessive alkalinity of modern papers.
- Platinum prints are 2 to 4 times more expensive than palladium prints.
- Platinum prints demand high processing temperatures – 50+°C – if maximum quality is the objective.
- Platinum prints have problems with oxidizer concentrations above 2%; at that point, they become quite grainy.
- Platinum prints have less trouble to stand the clearing process.
- Platinum prints are appreciated for their cold tones.
11.9 Platinum tones with palladium salts?
- Typical platinum print tones can be reached when using palladium salts; you will even get better blacks and contrast.
- All paper types can be used provided they are sized with one or two layers of warm gelatin. Use about the same volume as for the emulsion, coat with brush and heat dry. Gelatin preparation: recipe 2, chapter III.
- It is advised to use Arches Platine paper, processed in sodium citrate with dichromate at the lowest possible temperature – 7°C or less.
12. Clearing
This manipulation aims at eliminating the ferrous oxalate remaining in the print after development by means of a very diluted acid: hydrochloric acid, oxalic acid, citric acid, phosphoric acid or E.D.T.A.
(Ethylene diamine tetraacetic acid) is the acid recommended and marketed by Bostick and Sullivan. It is not easy to find it in France, and it is quite expensive. (Not tested)
12.1 Classic method
- For platinum prints, prepare three baths of diluted hydrochloric acid, from 0,5 % to 1 %, i.e. 5-10 cc of acid by liter
- after development, put the print for 5 minutes in the first bath, agitate continuously during the first minute, and then 3 or 4 times per minute
- repeat this twice, 5 minutes each time, in 2 fresh baths
12.2 My method ✌
- Prefer oxalic acid to other acids. It is effective, less dangerous than hydrochloric acid, and it has no effect on the palladium metal
- The concentration is about a coffee spoon or more oxalic acid for 500 ml of water. Precise weighings are unnecessary to use water at roughly 50°C. Warm tap water will do
- For Arches Platine, when acid baths stop clearing any further the print from its ferrous oxalate, use a sodium sulphite bath until clearing is complete. Concentration is not critical
- Examine the clearing progress by transparency, in front of a window by daylight. Do not use the acid baths more than necessary, as they might eventually weaken the image
- A persisting yellow stain might indicate that the paper or developer are too alkaline, or that the ferric oxalate is too old or polluted
It has to be noted however that this yellow stain was sometimes looked for by the early platinum printers for its aesthetic qualities, to the detriment of preservation.
13. Washing, Drying, Finishing – My Method ✌
- neutralizing the acids for one or two minutes with some diluted sodium bicarbonate will be sufficient. For washing, agitate and go through 10 water changes. The mechanical effect of washing too long in the tray would weaken the image
- Drying can be done at room temperature or with heat
- The prints can be flattened with a dry-mount press, or with the following technique, which produces superb results: after having carefully blotted it with a kitchen roll, put the damp print on a glass sheet. This has to be done carefully, as the damp surface is still fragile. Make sure it adheres. Fix the edges with Kraft paper tape. Let dry and finally use a cutter to remove the print. It will be perfectly flat and have a really nice velvety aspect.
- Retouching can be done as usual, and more specifically with watercolor. A particularly elegant solution is to rub a still wet test strip in order to have palladium particles getting off it and to prepare a mixture with them for retouching the print while it still is wet.