Print-out Platinum-palladium Printing
Last edited in November, 2016
We share this work freely, and only ask that the authors (Pradip Malde and Mike Ware) of the document be acknowledged. No part of this work may be used for commercial purposes without specific written permission from the authors.
- 1 Print-out Platinum-palladium Printing
- 2 What’s in a name
- 3 Overview
- 3.1 Health & Safety: Platinum Allergy
- 3.2 Chemicals for Preparing Platinum-palladium Sensitizer
- 3.3 Chemicals for Processing Platino/palladiotypes
- 3.4 Apparatus for Preparing Platino/palladiotype Sensitizer
- 3.5 Equipment and Materials for Coating and Printing Platino/palladiotypes
- 3.6 Preparation of Platino/palladiotype Sensitizer Solutions
- 3.7 Making up the Platino/palladiotype Processing Solutions
- 4 Procedure for the Platino/palladiotype
- 4.1 I. Choice of Paper
- 4.2 II. Choice of Sensitizer Composition and Image Colour
- 4.3 III. Choice of Print Contrast
- 4.4 IV. Mixing the Sensitizer Solutions
- 4.5 V. Addition of Surfactant to Sensitizer
- 4.6 VI. Coating Paper with Sensitizer using a Glass Rod
- 4.7 VII. Drying & Storage
- 4.8 VIII. Hydrating
- 4.9 IX. Exposure and Printing Frames
- 4.10 X. Negative Masking
- 4.11 XI. Wet Processing Procedure
- 4.12 XII. Finishing
- 5 Permanence & Stability
- 6 Summary of Platino-palladiotype Workflow
What’s in a name
Prints from the two precious metals may be made with platinum, palladium or a mixture of both. We propose, and will use the term ‘platinum/palladium’ as a way of denoting all of these recipes. The hyphenated form, ‘platinum-palladium’ is understood to describe a print made from a combined recipe of platinum and palladium salts, where the greater portion of metal in the finished print is platinum or platinum and palladium are present in almost equal amounts. By this logic, prints where palladium is the predominant ingredient should be called palladium-platinum. Most contemporary prints made with a combined recipe are rendered from a predominance of palladium and should, strictly speaking, be described as suggested here. We also refer to prints made with platinum or palladium as ‘Platinotype’ and ‘Palladiotype’ or when combined, as platino-palladiotypes. etc. Finally, the chemical symbols for platinum and palladium are Pt and Pd respectively, and we occasionally use these as a shorthand for the full names.
- platinum print or platinotype = a print made with just platinum sensitizer
- palladium print or palladiotype = a print made with just palladium sensitizer
- platinum-palladium print or platino-palladiotype = a print made with equal volumes of platinum and palladium sensitizer or a greater amount of platinum sensitizer than palladium sensitizer
- palladium-platinum print or palladio-platinotype = a print made with a greater amount of palladium sensitizer than platinum sensitizer
- platinum/palladium print or platino/palladiotype = a general way of referring to all of these recipes
Platinotype was invented by William Willis of Bromley in 1873; by 1892 it became the pre-eminent printing process for artistic photography. In 1916, the First World War imposed a ban on this use of platinum, so Willis devised Palladiotype as a substitute, but platinum paper made a come-back in 1920, surviving until Willis’s Platinotype Company was finally dissolved in 1937. For the next 40 years both processes fell into disuse, until revived in the alternative photography renaissance of the 1970-80s.
In recent years platinum-palladium printing has regained its place at the summit of alternative photographic practice, renowned for the subtly nuanced tonal qualities of its images, formed by totally permanent ‘noble’ metals in the matte surface of artists’ paper. Willis’s traditional platinotype and palladiotype were development processes, and capable of beautiful results in skilled hands, but they suffered from some chemical inconsistencies. The method described here employs a better-behaved iron sensitizer, derived from the ‘print-out’ platinum process due to Giuseppe Pizzighelli in 1887. Read Mike Ware’s technical comparison of the modernized version with the earlier processes.
This modernized version has some advantages in economy, accessible chemistry, and exposure control. Using the procedures described in these notes, platinum or palladium may be used individually, or mixed in any proportion, providing a choice of the image hue between neutral grey-black and rich sepia. A controlled degree of humidity is allowed in the sensitized paper to promote the formation of a printed-out image in platinum/palladium during the exposure, requiring little or no development. A carefully-devised clearing sequence ensures that all the iron is removed from the paper.
It is the responsibility of the users of chemicals to inform themselves about the risks, and to take appropriate precautions in their handling. Reference should be made to the Materials Safety Data Sheets (MSDS), which are accessible online.
The authors hereby deny liability for any consequent sickness, injury, damage or loss resulting from the use of the chemicals named herein.
Health & Safety: Platinum Allergy
Contact with ammonium tetrachloroplatinate(II), and other chloro-complexes of platinum, is known to cause symptoms of asthma, urticaria and dermatitis; some allergic individuals may become particularly sensitized to these biologically-active chemicals. The symptoms disappear on removing the cause: if you develop this allergy, then platinum printing is not for you – but you could still use palladium. Appropriately, ‘platinum allergy’ was first observed in 1911 as an occupational disease of photographic factory workers handling platinotype paper. Never touch the surface of platinum-sensitized paper or immerse ungloved fingers in the processing solutions. It is better not to store large amounts of dried sensitized paper. Platinum metal itself is not implicated in this – so take comfort that there is no risk in handling fully-processed platinotypes!
Chemicals for Preparing Platinum-palladium Sensitizer
Purity: General Purpose Reagent (GPR) grade ca. 98%
The quantities formulated below will suffice to make about 60 10×8 in. Pt/Pd prints
Substance, Formula & MSDS Quantity
Ammonium iron(III) oxalate (NH4)3Fe(C2O4)3.3H2O 30 g
aka ferric ammonium oxalate; ammonium ferrioxalate
Ammonium tetrachloroplatinate(II) (NH4)2PtCl4 5 g
aka ammonium chloroplatinite
Ammonium tetrachloropalladate(II) (NH4)2PdCl4 5 g
aka ammonium chloropalladite
Palladium(II) chloride PdCl2 3 g
aka palladium dichloride
Ammonium chloride NH4Cl 1.8 g
Water, purified, H2O 100 cc
(distilled, de-ionised, pharmaceutical, etc)
Tween 20™ C58H114O26 0.25 cc
aka polyoxyethylenesorbitanmonolaurate; polysorbate
Separate solution diluted to 10% or 5% v/v
Chemicals for Processing Platino/palladiotypes
Purity: General Purpose Reagent (GPR) grade ca. 98%
These quantities suffice to process ca. 60 10×8 in. Pt/Pd prints
Processing Solutions / Quantity
Note: Meaning of Solution Strength abbreviation:
X% w/v “weight per volume”: X grams of solute in 100 cc of solution
Ethylenediaminetetraacetic acid, disodium salt 5% w/v 2 litres
aka 1,2-Diaminoethanetetraethanoic acid, disodium salt; Disodium EDTA; disodium edetate;
dissolve 100 g of the solid in 2 litres of water
Ethylenediaminetetraacetic acid tetrasodium salt 5% w/v 2 litres
aka 1,2-Diaminoethanetetraethanoic acid, tetrasodium salt; Tetrasodium EDTA; tetrasodium edetate
dissolve 100 g of the solid in 2 litres of water
Sodium metabisulphite Na2S2O5 2.5% w/v 1 litre
aka sodium pyrosulphite; sodium disulphite
dissolve 25 g (a level tablespoonful) of the solid in 1 litre of water
Alternatively, sodium sulphite or sodium hydrogen sulphite (sodium bisulphite) or Kodak ‘Hypoclear’ powder may be used. This solution should be made up fresh for a day’s printing, and should not be stored and re-used.
Apparatus for Preparing Platino/palladiotype Sensitizer
- Pyrex glass beakers 2 x 100 cc
- Measuring cylinder 50 or 100 cc
- Scales or chemical balance sensitive to 0.1 g
- Glass stirring rod
- Conical filter funnel ca. 5-6 cm diameter
- Filter paper Whatman Grade #1 ca. 8-10 cm diameter
- Brown glass bottles 3 x 100 cc
- Hotplate (or bath of very hot water)
- Tungsten or low-level LED lighting to work under, not UV-emiting fluorescent or daylight.
Equipment and Materials for Coating and Printing Platino/palladiotypes
- Glass coating rod
- Blotting strips
- Syringes – at least 4, calibrated 1 cc, 2 cc and 5 cc
- Mixing vessel – small liqueur or ‘shot’ glass
- Glass plate – at least 6mm thick
- Spirit level
- Drafting tape or clips
- Print frame – preferably hinged-back
- Cat litter trays – for print hydration enclosures – with lids
- UVA light source, such as a domestic ‘solarium’ – facial tanning unit
- Plastic measuring jug 2 litre
- Processing dishes (5)
- Tongs or plastic gloves
- Drying line and pegs or drying screen
Preparation of Platino/palladiotype Sensitizer Solutions
N.B. The following sequence of operations should be carried out under dim tungsten or LED lighting, not UV-emiting fluorescent or daylight
Iron solution 60% w/v ammonium iron(III) oxalate
(Volume 50 cc)
- Weigh out 30 g of ammonium iron(III) oxalate into a small (100 cc) Pyrex glass beaker.
- Add exactly 33 cc of pure water (from a measuring cylinder) and stir well to dissolve the solid.
- The solution becomes cold, so gently warm the beaker in a bath of hot water (ca. 50°C) to assist dissolution.
- The solid will dissolve to form an emerald-green solution within 5 minutes. Check that the final volume is correct (50 cc).
(Any tiny residue of remaining solid may be ignored.)
- Filter the solution (Whatman #1 filter paper) directly into a clean, dry, brown glass storage bottle, and label appropriately. Store at room temperature in the dark: the shelf-life will be several years.
(If, after a few days, some white needle-like crystals (probably of ammonium oxalate) have appeared, re-filter the solution to remove them. This solution is close to saturation; if cooled below 20ºC for a length of time, green crystals may appear: warm gently and swirl to redissolve these.)
Platinum solution 25% w/v ammonium tetrachloroplatinate(II)
(Volume 20 cc)
- Weigh out 5 g of ammonium tetrachloroplatinate(II) and transfer into a small (50 cc) measuring cylinder
(You may assume that suppliers’ stated amounts are accurate)
- Add 18 cc of pure water to dissolve the solid by stirring at room temperature. Check that the final volume is correct (20 cc) in the measuring cylinder, and make up if not.
- Decant the solution directly into a brown glass storage bottle, labelled and dated.
(Any small amount of yellow precipitate may be ignored.)
- Allow the solution to stand for at least 24 hours before first use.
The solution should keep for a year or so.
Palladium solution 19% w/v ammonium tetrachloropalladate(II)
(Two options – depending on price and availability of chemicals)
Method 1 (Volume 26 cc)
- Weigh out 5 g of ammonium tetrachloropalladate(II) and transfer into a small (50 cc) measuring cylinder.
- Add ca. 15 cc of pure water to dissolve the solid by stirring at room temperature.
- Make up the solution with pure water to a volume of exactly 26 cc in the measuring cylinder.
- Filter the solution using a small conical funnel and Whatman Grade #1 filter paper, directly into an amber storage bottle, stopper and label it.
Method 2 (Volume 25 cc)
- Weigh out accurately 1.8 g of ammonium chloride into a 100 cc Pyrex glass beaker
- Add 20 cc of pure water and all the solid should dissolve easily.
- Heat the solution (ca. 70°C) and add 3 g of well-powdered palladium(II) chloride, a little at a time, with stirring.
Hazard! Wear a dust mask!
Keep hot and stir until all the brown solid has dissolved to give a very dark red solution. This may take up to an hour. Carefully view the solution from below to see if any solid remains.
- Allow to cool and transfer the solution to a small measuring cylinder, and make up to a volume of exactly 25 cc with pure water. Use some of this water to wash out any solution left in the beaker.
- Filter the solution using a small conical funnel and Whatman Grade #1 filter paper, directly into a brown glass storage bottle; stopper and label it.
This solution is stable indefinitely.
Making up the Platino/palladiotype Processing Solutions
1. Disodium EDTA (5% w/v)
Dissolve ca. 50 g of disodium EDTA in 1 litre (1000 cc) of tap water in a large plastic measuring jug with stirring at room temperature.
Capacity 50 prints 10″x8″ per litre.
If disodium EDTA is unavailable, and only tetrasodium EDTA on hand, the latter may be effectively converted to the former by the addition of citric acid, (C6H8O7) to the extent of 16 g of citric acid to each 50 g of tetrasodium EDTA. The presence of the citrate ion can only assist the clearing.
2. Sodium disulphite (2.5% w/v)
Dissolve ca. 25 g (one rounded tablespoonful) of sodium disulphite, (aka sodium metabisulphite, Na2S2O5) in 1 litre of tap water.
Use this solution for one printing session only and discard it.
Do not store.
3. Tetrasodium EDTA (5% w/v)
Dissolve ca. 50 g of tetrasodium EDTA in 1 litre of tap water with stirring at room temperature.
Capacity 100 prints 10″x8″ per litre.
Procedure for the Platino/palladiotype
I. Choice of Paper
Do not use papers that are alkaline-buffered with chalk (calcium carbonate). Best results will be obtained on unbuffered papers such as:
- Arches Platine (2015 batch)
- ‘Buxton’ or ‘Herschel’ papers handmade by Ruscombe Mill
- Reich CT vellum
- Wyndstone Vellum
If buffered papers are unavoidable, such as Canson Lavis Technique, Fabriano Artistico, or Whatman Watercolour, they should be pre-treated in a bath of dilute (5% v/v) hydrochloric acid or sulphamic acid to destroy the chalk, then washed.
We suggest not using gelatin-sized papers for platinum-containing prints: gelatin inhibits the chemistry of platinum metal formation. They may be used for pure palladium prints, on which gelatin has no adverse effect. Papers sized with Alkylketene dimers (AKD), such as Aquapel™ , or with alum-rosin are suitable for platinotype.
For prints up to 10×8 in. or A4 in size, a paper weight of 160 gsm (grams per square meter, g/m2) is adequate. For larger prints of A3 size, a heavier weight of 240 gsm, or more, will minimise cockling and “bellying” of the coated sheet due to the stresses set up by the hydroexpansion of the cellulose fibres in the wetted area. The sheet will contact the negative better, and be more robust in wet handling.
II. Choice of Sensitizer Composition and Image Colour
Platinum and palladium solutions may be used separately, or combined in any ratio in the sensitizer in order to fulfill your wishes for the hue, contrast and metallic composition of the finished print:
Palladium yields Van Dyke brown or sepia tones and a softer image, i.e. a longer exposure scale, with great delicacy in the high values. The tones are warmer on gelatin-sized papers than on Aquapel-sized. When well-humidified (RH 80%), near-neutral tones can be achieved with pure palladium, provided that no surfactants (wetting agents) are added, and that exposures are not too brief.
Platinum yields neutral tones and tends to provide a slightly higher contrast (shorter exposure range) than palladium, and greater maximum density; but the overall speed of printing may be slower, depending on the purity of the paper, which is paramount.
Platinum-palladium mixtures combine their characteristics proportionally, and offer a useful compromise, but leave some uncertainty about the exact composition of the image.
The characteristics of some sensitizers – their colour, relative speed and exposure scale – are summarised in the Table below, showing their dependence on the Relative Humidity (RH%).
Characteristics of Print-out Platinum-Palladium Sensitizers
- The Relative Speed is arithmetic, referring to middle tones.
- The Exposure Scale runs from density fog+0.04 to 0.9Dmax
- Development is in logH units (0.3=1 stop). 0 is total print-out.
- Note that these parameters will vary with the choice of paper.
III. Choice of Print Contrast
Having prepared a negative of approximately the right density range, ca. 2.2, the contrast may be fine-tuned in the printing process by two main controls: the ratio of platinum to palladium in the mix, or by regulating the humidity of the sensitized paper before exposure.
The printing exposure scale values in the Table indicate the effects of these controls.
Mixing the platinum and palladium solutions in the ratio of about 3:1, gives a sensitizer with a colour, contrast and speed that are fairly constant over wide variations in humidity (RH 40-70%), and with a long range of well-graduated neutral tones, and a good Dmax.
IV. Mixing the Sensitizer Solutions
• For a palladium print mix equal volumes of the iron and palladium solutions, which may be coated immediately.
• For a platinum print mix equal volumes of the iron and platinum solutions; for highest Dmax let the mixture mature for one hour in the dark at room temperature before coating.
• For a platinum-palladium or palladium-platinum print you may combine the platinum and palladium solutions in any proportion: then add the mixture to an equal volume of iron solution. Preferably let the mixture mature for one hour in the dark before coating.
Mixing should be done at room temperature under tungsten lighting.
These small volumes are conveniently measured and delivered by means of disposable calibrated plastic syringes (without hypodermic needles!) of capacity 1, 2 or 5 cc. Dedicate a separate syringe for each solution to avoid cross-contamination of the stock solutions, and use a fourth syringe for delivering the mixed sensitizer onto the paper. A small liqueur glass makes an ideal mixing vessel – provided you give up drinking out of it! Mix the solutions well by drawing the liquid gently in and out of the delivery syringe three times. To ‘mature’ a solution before coating draw it up into a syringe to minimize evaporation, and leave in a dark place for 1 to 2 hours.
V. Addition of Surfactant to Sensitizer
Absorbent papers may not require any additional surfactant (wetting agent), but some hard-sized papers, such as Buxton, may yield a better, more uniform coating if a surfactant is used.
Tween 20™ (a non-ionic surfactant) may be added to the sensitizer solution before coating to produce a final concentration of ca. 0.25%. Add one drop (0.05 cc) of a 5% stock solution of Tween 20™ for each cc of sensitizer and mix well (or one drop of 10% per 2 cc).
Do not add Tween to the stock sensitizer solution: it doesn’t last very well, and the appropriate amount will depend upon the paper. Tween may interact unfavourably with gelatin-sized papers. Tween also tends to promote a warm colour in palladium.
VI. Coating Paper with Sensitizer using a Glass Rod
All manipulation of the sensitized paper can be carried out under dim tungsten lighting: avoid fluorescent or daylight. Room temperature should be normal (18-22°C), if too low the sensitizer may crystallize.
For the coating implement we recommend a thick-walled glass capillary tube, rather than solid rod, because the former is usually manufactured to higher standards of straightness. An external diameter between 6 and 12 mm is suitable. The end portions of the rod should be bent at an angle using a powerful gas torch; a bicycle handlebar shape is simple and ergonomically effective in use. The centre portion of the rod acts as the spreader and is equal in length to the width of the coating area; the limbs serve as handles. This implement must be kept scrupulously clean. An appropriate rod will be needed for each format to be printed.
Coating by the rod method will require ca. 1.5 cc of sensitizer to coat an area appropriate for a 10×8 in. print. Brush coating consumes more and is expensively wasteful. Paper stored at low relative humidity (less than 50% RH) may imbibe excessive amounts of sensitizer and coat unevenly. Before coating, it may be advantageous to pre-humidify the sheet to 70-80% RH (see section VIII. Humidifying, below).
- If necessary, cut or tear your sheet of paper to a size that allows generous margins around the picture area, for ease of future handling, but still fits the printing frame.
- Mark the sheet of paper lightly in graphite pencil at the corners of the area to be coated – a template helps. The coating dimensions should be 1 cm larger than the negative to allow for irregularities.
- Check that the surface, ideally a thick sheet of glass, on which the paper will be coated is level on the left to right plane; gauge with a spirit level and adjust it if necessary by inserting spacers below the glass plate.
- Tape or clip the sheet lightly, at top and bottom, to a very flat level surface: a heavy (6 mm) glass plate is ideal. Use a low-tack tape such as Scotch Removeable 3M811.
- Dust off the surface with a blower brush.
- Draw up the mixed sensitizer into a syringe of appropriate size, and adjust it to the required volume, reading from the bottom of the plunger. Calculate a trial volume from the average specific coating volume of 25 cc per square meter of paper area.
- Point the nozzle of the syringe at the bottom left mark, and, using both hands for maximum control, expel the liquid slowly and gently, in an unbroken strip of sensitizer as you move it steadily from left to right across the width of the coating area. For steadiness, touch the paper lightly with the syringe nozzle, but avoid skin contact with the paper. Do not be too slow or fussy – irregularities will even out in the coating.
- Hold the coating rod with one end in each hand, and place the straight central portion onto the paper parallel to, and a little below, the strip of sensitizer. Then, with moderate pressure, push the spreading rod up into the strip of solution. Pause briefly (2 seconds) while the liquid distributes itself uniformly along the length of the rod, then steadily push the strip of solution up the paper, like a tiny tidal wave running in front of the rod.
- When you reach the pencil marks at the top of the coated area, ‘hop’ the rod over the strip of solution and pull it back to the bottom of the coating; then hop over the sensitizer strip once more and push it up to repeat the spreading. Just four passes over the paper should suffice for its surface layer to become saturated with a uniform coating of sensitizer. The first pass should be made quite rapidly (3 or 4 seconds) applying moderate pressure to ensure complete wetting of the surface. The last three passes as slowly as possible (10 to 15 seconds each) with very little pressure applied, to allow maximum absorption. At the end of the fourth pass, drag the spreader below the picture area with any excess sensitizer. But if much excess solution remains you can apply two more passes.
- Gently lift off the rod, and soak up any residual liquid left at the bottom of the coating with a clean strip of blotting paper.
In future coatings, try to “fine tune” your exact coating volume on the basis of experience with your chosen paper, in order to minimize waste. See some illustrated instructions.
VII. Drying & Storage
It is simplest to let the sensitized paper dry at room temperature and RH, in the dark, for about an hour. Shorter times are possible, but very humid paper may not lie flat due to fibre swelling, and may damage precious silver-gelatin negatives unless they are protected by a very thin sheet of Mylar film (20 micron). Alternatively, allow a few minutes for the sensitizer to soak in, until the paper surface appears non-reflective, then heat-dry it with an air stream at about 40°C for ca. 10 minutes.
The sensitized paper should be used within a few hours; otherwise, it must be stored in a light-tight, air-tight container, in the presence of a desiccant such as silica gel or anhydrous calcium chloride, below 10% RH, in order to prevent chemical fogging. Paper may be stored for six months in this way without loss of quality.
The key to the print-out process of platino/palladiotype lies in controlling the humidity of the sensitized paper just before exposure. The effect of ambient RH on the extent of print-out, colour and contrast is summarised in the Table above, from which you will see that optimum results are obtained between 50% and 80% ambient RH. Below 50% RH there is only partial printout and considerable development, above 80% RH the maximum density of the image may tend to weaken because the sensitizer diffuses too deeply into the paper. There are three convenient methods for introducing a controlled amount of humidity into the sensitized paper, a process which we refer to as ‘hydration’.
- Ambient Hydration: If you have a hygrometer, you can simply make use of the prevailing RH (if suitable) to achieve a predictable result by hanging the paper in a dark place at room temperature (ca. 20°C) for an hour or two before exposure.
- Water Tank Hydration: A more accurate method of humidifying is provided by using a water-based hydration tank. This may be easily made using a tray with close-fitting lid, in which the paper may be placed face down, over, but not in contact with, purified water at exactly the same temperature as the ambient temperature. Ideally, this should be at 20 to 21C, or 68 to 70F. This will, within 2 to 3 minutes of closing the lid, generate an atmosphere of constant, known relative humidity close to RH 100%. Cat litter trays are ideal for this purpose; photographic dishes are too shallow and have a lip which makes sealing difficult. The sheet of sensitized paper is held securely on the underside of the lid by two strips of self-adhesive magnetic tape and matching magnets, which is quick, clean, and does not mark the paper. Both a steady ambient temperature and the timing of the humidification is critical: from 5 to 15 minutes for a warm-toned result; a longer humidification of 30 to 40 minutes in the water vapour will yield fuller print-out and a colder image tone. Humidification at RH 100% for more than one hour may lead to weakening of the image density, and clearing problems. Over-humidified paper is also more likely to damage negatives during contact printing.
- Salt Hydration: The greatest control is provided by a hydration tank with a saturated aqueous solution which provides an atmosphere of constant, known relative humidity. A setup similar to that described the Water Tank Hydration method is used, but water is substituted with a salt. Actual volumes will depend on the size of the hydration tray, but add just enough water to the solid salt so that after an hour or so, there should be excess solid salt in contact with its saturated solution. It is also important that the paper should be evenly exposed to the vapor. Ambient temperatures may vary and are not critical, but it is good practice to sustain a steady room temperature. The time of exposure in the humidifying tank should not be less than half an hour, to achieve evenness; the upper time limit is not critical and can be as much as two hours. The most useful saturated solutions are:• ammonium chloride which will generate an atmosphere of RH 80%• common salt (sodium chloride) which will generate an atmosphere of RH 76%• calcium nitrate tetrahydrate which will generate an atmosphere of RH 55%
IX. Exposure and Printing Frames
Negatives should have a long density range (in the UV): at least 1.8 for pure platinum and as much as 2.4 for pure palladium, to produce a full tonal range in the print.
Exposure is a between 2 and 10 minutes under an average 120 Watt fluorescent UVA light source, with peak emission around a wavelength of 365 nm, such as a facial solarium. With an 800 Watt HID lamp and digital negatives, exposure is ca. 40 seconds; such a short exposure may produce warmer tones with palladium.
Since this is substantially a print-out process, a hinged-back contact printing frame enables inspection of the intermediate result: under conditions of full print-out (prints hydrated at 80% RH or greater) you can continue exposing until the highlight detail is resolved; the shadows will not ‘block up’ totally, like development papers, because the printing-out process has a self-masking action in regions of high print density.
X. Negative Masking
It is preferable to mask the borders of the printed area from exposure, rather than darken them to show the rough edges left by passes of the glass rod or by brush strokes. There are three reasons for this preference: aesthetic, technical, and practical.
Aesthetically, it seems unnecessary to ‘show the brushmarks’ in order to prove that it’s a handmade print – connoisseurs will already know that anyway. Moreover, an erratic black border provides a strong peripheral distraction from the image content. The formal, geometrical qualities of the rectangular frame have the time-honoured virtue of being unpretentious.
The technical reason is most important: the masked border that has been coated with sensitizer, but remains unexposed, provides a direct visual test of the completeness of clearing excess chemicals from the print during the wet processing, by comparison with the uncoated paper margins. If the borders are not masked, but exposed and darkened, one can never tell if the print has been properly cleared. This can be a cruelly demanding test – but is very desirable for permanence!
In practical terms, if there is a large non-image area of redundant sensitizer which is heavily exposed, the dense photoproduct may “bleed” during wet processing, into light image areas like sky, and ruin the print. Moreover, an unnecessary excess of CO2 gas will be produced. Masking the print with ‘Rubylith’ or black polythene costs nothing except a little care and precision – the hallmarks of good craftsmanship.
XI. Wet Processing Procedure
An optional step: Post-exposure hydration for 1-2 mins
This enhances the gradation in the high values, especially if print-out is not complete. Use the Water Tank Hydration method, exposing the print surface uniformly to water vapour, or manually suspend the print over a tray of warm water at ca. 100F / 40C. Once complete, continue with print processing as described below.
Promptly and fully immerse the print in the following wet-processing baths – face down if the paper floats, face up if not – with intermittent agitation:
- Develop in disodium EDTA (5% w/v) 10 minsIt is important that this first bath should be acidic, around pH 4. Do not use tetrasodium EDTA. Its capacity is ca. 60 10×8 in. prints. When spent, this bath should be saved for recovery of precious metals.
- Rinse in fresh water half min
- Clear in sodium metabisulphite (2.5% w/v) 10 mins. This sulphite bath does not keep, so should not be stored and re-used, but made up fresh for each printing session.
- Rinse in fresh water half min
- Clear in tetrasodium EDTA (5% w/v) 10 mins. The capacity of this bath is at least 60 10×8 in. prints.
- Wash in running water for a minimum of 30-60 mins
- Drain face out, on a near-vertical sheet of Plexiglass 10 mins
- Dry at room temperature on a horizontal plastic / fibreglass screen.
N.B. Do not allow the processing solutions, especially bath 2, to come in contact with your skin: use print tongs or gloves.
Examine the print for any yellow stain of residual iron in regions of unexposed sensitizer; this is more conspicuous under a bluish light. If present, prolong the #5 tetrasodium EDTA clearing bath.
In a 100% platinum print the print-out is less vigorous, especially at low RH. Better quality may result if the more energetic, platinotype developer, 30% w/v potassium oxalate solution, is used as a first, development, bath, and then followed by the above sequence.
The print is easy to retouch using permanent watercolour pigments.
Permanence & Stability
Platino/palladiotypes are highly lightfast and robustly resistant to all contaminants likely to arise in a normal environment.
Summary of Platino-palladiotype Workflow
- Select and cut paper, choose side, mark up coating area, make printing notes as you proceed
- Mix sensitizer: measure and mix equal volumes of iron and platinum/palladium solutions; add Tween to ca. 0.2% if needed
- Coat paper: 1.5 cc per 10×8 in. 5 ‘passes’ of rod
- Dry: 1-2 hours at room temperature, or in a 100F / 40C airflow for 10 minutes
- Hydrate the sensitized paper: in controlled RH box (80% for full print-out)
- Expose: to UVA source until highlights just visible
- “Post-exposure Hydrate” the print for 1-2 minutes
- Develop and Clear #1: Disodium EDTA 5% for 10 minutes
- Rinse in water half minute
- Reduce and Clear #2: Sodium metabisulphite 2.5% 10 minutes
- Rinse in water half minute
- Final Clear #3: Tetrasodium EDTA 5% for 10 minutes
- Wash: at least 30 minutes
- Drain, Dry and press flat